You're filling a predefined space in her life. It is a known size... If it doesn't seem to be a good fit for you, I doubt you can do much to change that.

I'm a "single" mom (I'm not single, but my partner is not my child's father). When I was dating I could only go out on certain nights, and no one stayed at my home when my son was home. Until I met my partner. For him I was willing to make changes. Not just willing, it felt natural. If she's not willing to make changes (especially with kids 16 & up) it sounds like maybe you aren't the one.

In my opinion, 16 is not a grown up child. I don't think that I would have thought it appropriate to have someone sleep over with a child that age in the house either. The home is their only home. They need to feel comfortable in it.

My kids always came first. I barely even dated as a single parent. It's not really fair to them.

When you take on a partner with kids - you take on the whole package - for better or worse. I hear that you love her, but I also hear a somewhat clingy attitude. If you don't handle loneliness that well - it's not her job to fill it all in. Might you be too focused oh her ?

If a closer, one-on-one situation is the only one you'll be happy with, this woman may not be able to provide that right now. Only you can decide what you're willing to tolerate.

It sounds as if her children are in control and she likes it that way. Eventually this may change the way you feel about her, but it's doubtful that she will change the way she behaves. The ball is in your court.

Sounds to me like she needs to put her foot down with her kids, but you need to put your foot down with her as well. It’s time to let her know that she needs to talk to her kids and enforce some ground rules when it comes to her relationship with you, or you’ll have to move on with your life without her as a part of it.

So long as you are not being abusive or neglectful to them or their mother, and so long as she is dividing her time fairly between you and them, your relationship with their mother is no more their business than it is anybody else’s. It’s long past time to make that fact known.

You say the children are grown up...but how grown up? What are their ages? I presume that they will at some time leave the nest to make their own way in life, and become independent adults, but it’s just a matter of how long that is going to be. After three years of being in a relationship with their mother, and presumably having some sort of dialogue wirh them...even though you have indicated they haven’t made life easy, I think you should actually speak directly to them. Tell them how you feel about their mother in frank terms, that you love her and wish them to have a proper relationship, which includes staying the night. I can understand that she doesn’t wish to upset her children, but it’s ureasonable of them to expect to be able to keep their mother from having a mature and loving relationship.. It is time to speak out, or just resign yourself to a very unfulfilling relationship for years to come.

Doesn't sound like she’s alone.. but you are. It’s up to her to explain things to her kids, that’s life. Does she feel she’s being ‘protective’ of them by not allowing them to feel the least bit uncomfortable?

When my parents split it wasn’t all that difficult to see they planned to continue their lives, and I don’t think it scarred us..

There are just two things a parent can give kids: love and wings. The second is harder. Sometimes you have to staple the wings on their back and give them a shove.
This is the work this woman is having trouble with. I doubt you can help her with it. They would all just resent you. I think you have to accept the situation and decide whether you really want to be part of it for a long time to come. You can't change her, you can only change you.