My wife believes that she should believe. She does not actually believe in God she just pretends to and professes to because it's a good idea. I have known her for over twenty years and can tell you she actually does not believe but does not even know it. I can't tell her this, it is something she will have to discover on her own. She is so worried about social stigma I doubt she will ever give it any thought.

I won't even go out with a believer, much less build a relationship with one. I greatly prefer people who live their lives rationally, and simply cannot relate to most theists very well.

My first non-marriage was to a heathen and it worked okay for the time it lasted. But we were still pretty young.
My only marriage, which came much later in life, was to a Born Again, and I have to admit I wasn't fully informed (ignorant) as to all the ramifications at the time. I remember telling my mother, a devout protestant all her life, and her reaction being a very guarded sigh.
We talked about our different beliefs early on and I thought we had agreed to allow each other space. It didn't bother me at all if she wanted to read her bible, go to church, etc, as long as it didn't interfere with our marriage. That lasted about 5 years and then it began.
She tried to convince me that we couldn't be together in an afterlife if I didn't firmly believe in God/Jesus. We had several of these conversations until I felt we had talked it to death, so to speak. I couldn't talk to her about it again. It got to feel like I had to compete with God in my own house. Very uncomfortable. The last time she tried was about 3 or 4 months before announcing that she wanted a divorce.
As time went on, she became more and more involved, even dragging me to a few church related functions. I wasn't comfortable there, but she was my wife and did ask me to go with her, so I did. She would invite some of her christian friends over to the house which I didn't mind, and we had some fun times and good conversation together. But she herself was getting deeper and deeper into it. I should have identified with those signs.
I'm sure this concern about being alone for all eternity is largely the reason she divorced me. I was her fourth husband (yeah, I know, right?) She's now working on her fifth who I'm told is also a Born Again. Imagine that.

For some people, religion is part of life. For others, life is part of religion. Avoid the latter at all cost.

My husband is a believer but he's lax. He hasn't been in a church other than for a funeral or wedding since we met. I can work with that. We have had a few religious discussion but nothing heated or antagonistic. He told me once that one of the reasons he loved me was because despite my not being Christian I was the most caring and sane person he's ever met... considering he was raised in a Southern Baptist community... well... couldn't help but turn an eyebrow to that one. I'm still not sure he caught it but we never spoke of that again.

I have had a difficult time negotiating with a former partner that chalked his passivity up to his Catholic beliefs. I can't have a productive conversation with an imaginary being as an invisible participant. It has often been a way of not taking personal responsibility for one's actions. That said I will not put myself in that position again.

In my experience, it depends on how strong your own unbelief is.

My two relationships that were with non-believers (or otherwise not religious at all, even if not atheist) were the two best relationships I had. And the ones that ended with the greatest heartache. Go figure.

My last relationship was with a believer. As I've said here before, I will never ever ever be with a believer again. Through NO fault of his, it felt like I was stifling a big part of my true self for three years. Not to mention the time away from life that his going to church took. Not to mention the $5,000 a year in tithing from our joint account. And, not to mention the bibles and crosses in the house. I seriously don't get the need to be show-offy with religion. And to ME, displaying bibles, crosses, and making your grace before meals known to others, is show-offy.

Never Again. Life is too short.

I dated a Pentecostal once. I remember one time a friend of hers overdosed and died and she told me her friend was in Hell. I ended the relationship not long after that.

Mind your own business and don't push your non belief at them. My wife is a Catholic... yep... I just don't make those non believer remarks in her direction... it stays great that way. In a new relationship I would open up about it.. that's being honest. You'll hear that later if you don't ...

Usually pretty short-lived.