So sorry you are having to deal with this. I have some thoughts about your situation. One thing you haven’t mentioned is if you live with him, right now. Just curious. If you are, he is getting the "best of both worlds" now. You know the saying out there involving the words, cow -milk- free).
Personally, I couldn’t stay with someone who wouldn’t be willing to commit. But I need to disclose that I feel I’m a pretty religious person. So marriage is pretty important. I don’t know where you stand on religion.
"But…as someone else mentioned in another post…it is like a Catch 22. I love the person who is committed to me, who values my happiness enough to make a few sacrifices, who is a mature adult that I respect. Yet if he is really edging closer to 40 and unable to do this for me, then, some of the qualities that make up the person I love seem like they come into question. And I have to ask, is he really the person I thought he was?" It doesn’t seem like he’s the person you were hoping he’d turn out to be. (Whether or not he is the person you thought he was.) You want marriage, if he does not… and if you are interested in kids, and he is, unenthused…….. then you two don’t have as much in common as you really need, to maintain being a couple.
Or…am I being unfair? Is love love, no matter what, with or without a ring, and something you fight for at all costs? Can a wonderful, mature man who is willing to really take my needs into consideration still be a man who just can’t get married, for whatever reason? You aren’t being unfair. You want what you want out of life. You shouldn’t need to settle (which is what your mom is advising that you do.) Sure, love is love, but as the song goes, "Sometimes love just ain’t enough." A lot of people who love each other, break up, because they are not on the same page, at the same time. If you stay with him, you will soon come to wonder what else might have been out there? Would you have met someone else, gotten married, and had kids? You will always be wondering. You won’t truly be happy if you stay with him. You might feel safe, or grateful to have someone, but not really happy. (And therefore, also, frustrated, angry, resentful). I can understand if you’re nervous that you might not find someone else, while you still have time to have kids. But if you stay with him, it’s likely that you won’t have kids anyway. (I think that is some of the fear your mom has. Not wanting you to be alone. "Being with someone who gives you 50% is better than being with no one =0%." The problem with that is that all you will get is 50%. You can’t try for 100%, EVER.) And really, if you and your Boyfriend or Best Friend are meant to be together, in the end, I think you’d end up together again.
As for can men really not want to commit.. I think some men have issues with wanting to commit. I used to date someone whose parents got divorced when he was a teen, and felt that no matter how happy your marriage is, you can split up at any point. That was his perception of his parents’ marriage. I guess guys can be against the institution of marriage, but I have a hard time wrapping my brain around that. I kind of wonder if they really are just scared of officially committing to one woman. I don’t know if he’s scared to commit to you specifically, or saying yes to one woman forever, regardless of who it is. But I’m not sure it matters. Either way, it is not the way you want to live your life.
Would you want to be sacraficing and giving your life to someone, who would feel uncomfortable being with you if he didn’t have the freedom to dump you if "something better" comes along?
Good luck. I wish you nothing but happiness.