What you basically said is your girlfriend told you she loves you, wants a family with you and wishes to spend her life with you; and you rejected her multiple times. So, you let her know again and again you don't see her as your wife, future of your (potential) kids and you don't want to spend your life with her... also multiple times.

I'm sure your wife is a great person, but I would have ended things after the first rejection. Many people do that, including men. I'm not sure why would anyone stay with a person who told them they don't want to commit and don't love them enough to start a family together. The fact that she's your wife of 18 years means you're super lucky she didn't pack her stuff and left. It may also mean she didn't have enough confidence to leave and find a man who actually wanted to be with her, as opposed to someone she had to propose so many times and get rejected - which isn't just awful, but humiliating for her. I hope your kids won't know about how many times you humiliated their mother.