It's hard to imagine a guy being faithful to the same person for many, many years, but it does happen.
Kids bind the entire thing together, because it becomes so much about them, not just about you.
I have a lifelong friend for over 60 years and he and his wife have somewhat happy (other than when he got caught "funding" a hooker for gas), for over 40 years, but they never wanted kids. Nothing wrong with that, but I always tell him, "It's a good thing your mom and dad didn't feel that way."
Anyhow, when I was talking with his wife she was astounded that everything I talked about was primarily my kids.
Photos on the wall, how they are doing, etc. She said that is so cool, and now when she and her husband are older, its sad they have no one to care about or care about them.
People who marry, and choose not to have children, live lives that are all about themselves. It's a choice.