As an atheist since 13, nearly all of my friends are Christians. We don't talk about religion. They love me for who I am.

To answer the first part is a situation very similar to how democracies fumble once they've just ousted their dictators. My advice the void can only be filled or erased by stepping up to be responsible for oneself and one's actions. The latter is tricky because neither would they acknowledge the transition to non belief nor accommodate differing opinions. I think slowly reduce time spent with them on the religious front and associated activities and maybe they could adapt to your missing presence when it comes to matter of belief.

Lot was told but I will give my opinion
Lets go by parts

Void of God:
Read a lot the authors that advocate for a science based world. Sagam Hitchens, Dawkins etc. They have a realistic and at the same time poetic view of the world. As you understand more the world we live and how our biology and mind works you will fill this void. I know the feeling of being free and have no cosmic nany to take care of you anymore! It is frightening but at the same time the possibilities are amazing!
Plus this community is amazing, stay here for some support.

Relationship with family:

Well that depends on how catholic they are. By the cannon law an apostate should be excommunicated and if the priest don't do it the priest should have some punishment also, and any other catholic should denounce you for the priest. Once you are excommunicated any catholic should ostracize you.
(How do I know it? I used this law to get away from any formal ties with the church and when my family bothers me I tell that I will call the priest and tell they still talk to me).
But if they are not completely brainwashed, you just need time to show that you are a good person and you don't need god to be a good person.

Recovering catholic here as well. Never felt that void you mentioned. In fact, I felt the void while I was a catholic. I always felt that God I believed in was MIA. My friends and family were always understanding of my atheism. My mom and I made a deal: I will go through with the confirmation before leaving the church and she would never talk to me about religion. We both kept our promises.

I fill the void by focusing on the values instead of on the mythology, and I manage relationships by focusing on the values instead of on the mythology. If God is love, then love is still permissible for literalists and figuratists alike. If they forget, you can gently remind them.

In my early 20s I realized the indefensibility of belief in the existence of an all-powerful, all-knowing, eternal creator and directer of the universe(s). For a few decades I "filled the void" with hope for the future of humanity. Lately, globalism and its facilitation and encouragement of the propagation of the cruel Islam political ideology has seriously undermined that hope.

By realizing that it's gonna take a lot of time in both regards and consistent resistance. I was raised Catholic, quit believing after my mom forced the sacrament of Confirmation on me and I still have debris from their programming from over 50 years ago. But I also like myself and the world more without that baggage.

I stay away from conversation about religion and no gap for me

Let me offer a suggestion ... thoroughly examine your old beliefs and redefine your terms a bit. I am pretty convinced that the "god" of abrahamic beliefs was originally intended to be a personification of the universe as a whole. Once I came to that realization then my anger towards churchies subsided and I could sympathize with them for their ignorance. Further, at this point I found that I could still have faith in "god" through Lao Tzu and an emphasis on balance. I began to see things all as a cycle and when bad things happened I had faith that good was around the corner. You don't have to lose faith altogether - just focus on things that aren't mystical bullshit.

Hello and welcome. Do check out the groups if you have time, there is something for everyone. (I would not be surprised if there was an ex-catholic one.)

I wasn't raised Catholic but in a very religious Protestant home where we went to church every Sunday, at a minimum.

My journey from believer to atheist took a little over a decade; and the hardest part was accepting that my mother was wrong and losing a connection with her and other family members. However, I never once felt a "god void."

Knowing that hell is not real, that there is no cosmic overlord, and learning that everything is connected atomically/chemically has allowed me to experience a sense of connectedness and serenity that I never experienced as a believer; and I was a true believer--I just didn't like some of the things I believed and had to question them.

I have not worried about it. I enjoyed being without the bs so much i never give this any thoughts. Not an issue with me. I speak to them when spoken to, and vice versa..i guess i was just me. I have aquaintances, not particulary friends. What is a friend? Someone that cares enough about you to stay friends...
I had a few friends, not anymore. Seems religions and beliefs got in the way to much, so i just fade away into the sunset.
The relatives do not speak to me much. Thats ok, i don't need to hear it.

Sorry you feel a void in your heart without believing in God.

At 13, I became an atheist when I realized the Bible is just a book of stories or fables written by men. Have always been a skeptic.

I find joy and meaning in life with volunteering, reading, hiking, helping others, and being a mother. Hiking is a transcendent, uplifting experience for me. I have fun every day.

I can't help you with the void as I've been an atheist since my early 20's (questioning since my teens). As for handling religious relatives and friends.... just don't talk about religion.

I have an evangelical sister and a fundementalist best friend (and her family). We both respect each other's view on religion and leave it at that.

If you are a true believer in reality, there is not a void.

Managing friendships with people who are members cults, such as: Catholic, very difficult and sometimes dangerous, therefore as general rule a non-involvement policy is best, with few exceptions to that rule.

You are welcome to contact me, if you wish for the discussion on this subject. Or, you can contact me for the sole purpose of making a new friend....

Convert to the Church of The Flying Spaghetti Monster! Then explanations or replacements become unnecessary...

The god taught in the RC schools my occasionally violent father sent five children to was sadistic and selfish. I kicked the monster out and needed the void his absence left.
Before my father died he knew all five of us had quit. At 89 I know a few elderly Catholics and they behave in ways too strange to describe in the time I now have.

you might just be open to redefining your current def of "God," after all I said "you are elohim," so Yah might get larger rather than smaller, so to speak, and as for getting along with Catholic relatives hey Catholics are awesome! At least at many things, "service" is actually a verb and not a noun to them, etc? So iow seek where you agree, and maybe overlook where you dont?

Just getting a better than basic grasp on the science, especially the branches that believers will try to distort to prove their god exist.

Some good starting points on YouTube is potholer54, and Arron Ra.

As for the family and friends. Some I don’t tell, others I set clear boundaries concerning religious discussions.

If the don’t like it, chances are you can create your own family of friends. There are literally billions of other social opportunities. That’s what I did.

Deflection, I guess. By various paths I have converged on the Gnostics, or early Christianity. These perspectives look at scripture more allegorically and cast Christianity more as a process of enlightenment. Orgnaized reliion, especially Catholicism, has a secular overprint that leaves me bemused. Catholicism chose to structur itself on an imperial model.. Protestants, a business model. In every case, individuals outsource their spiritual development. I see these In conversation I seek perspectives to refine and explore my own beliefs. I seek common ground on the fundamentals but part ways on doctrinal questions. I get a "you are not one of us, but you listen" response that avoids open conflict and enables me to keep my distance. I see spiritual development as an exercise in sensing answers rathe than "The BIg Ask" of praying.

Never had it. If, in your case, you have, it's you who has to find a way to fill it.

As an ex-catholic myself, I came to my agnosticism through becoming educated in a non-catholic educational setting and through critical thinking courses and social science courses. So that when I finally realized I am agnostic, there was no void present. I actually felt relief and happy like the way I imagine born again christians feel when they discover their new identities.
As for the family issue, most do not understand what agnosticism entails and it is a mix between some trying to convert or convince me to come back in to the fold with those not talking about religion at all with me--- probably because I'd be candid with them and might insult them and their beliefs if we were to discuss it! heh

About filling the void, i think that void is best spend using your knowledge about your past religion, and study/research how to try having conversations with like minded people with your formal beliefs. Look at it like this, you know what done it for you, meaning what things made you realize and start questioning your religion. Now try educating yourself in a way that you might be able to make it easier for someone you talk to and help in that way. Hitchens had alot of great information about CatholIcs. At one point, u really went after mother Teresa. I think her name is Mary Johnson, a former nun, has a great book about her life. She also did a speech at the American Atheists national convention one year, which by the way is coming up in April at Phoenix, AZ. hope this helps. Thanks.

You would first need to try to set up some kind of boundaries. Have a mutual agreement to either not talk about religion at all, or only talk about it at certain times. That's the best advise i can think of. Thanks and good luck.