Some of the posts querying the girlfriend’s love given the “brutality” or abruptness of the break up are baffling to me.
Obviously we can’t know for sure whether she did or not but to me she seems to have behaved with admirable maturity and dignity and nothing suggests she didn’t love him.
They had been together for 3 years and they were living together, - so not in the honeymoon period; not in a long distance relationship but living like a married couple. She wanted the next step and instead of being passive aggressive about it or playing games, she asked him about getting married. He could have reacted in a number of ways, the ideal from her perspective would have been to be thrilled and they’d have gone on to get engaged within a short time scale. Now if he didn’t want that then that’s fine. What happened is while he said he would want to in the future he didn’t want any silly timelines, not ready etc. that will have been lead in her stomach and a knot in her throat. At that point she could have “had a strop” in the words of some posters and ended it then but she didn’t. After that conversation they both know she wants marriage and they both know his initial reaction was to reject timelines and pressure but there was hope in his reference to some time in the future. They continued to live together for three months after this conversation.
Now I suspect that her hope was that he’d been a bit taken by surprise and reacted in the moment a laddish immature way but that he’d think about it and join her in wanting to commit and get married. Unfortunately he seems to have assumed she’d gone back in her box and accepted the honour of his hand in marriage was not something she has a say in. Three months of him knowing what she wanted and her not pressuring further; just living together as they had been and would in the future if they married.
She must have experienced a horrible creeping disappointment. She didn’t want to pressure or wheedle him into marrying her; to give him an ultimatum. It wasn’t about a wedding it was about them both wanting to marry each other and commit to a future together and he didn't want it. Of course she rejected his panic “shut-up-ring” offer.
I’m not surprised she couldn’t face Christmas with him; exchanging gifts, facing time as an established couple with his happy family and with hers.
If she broke it off after Christmas the OP and his defenders would be clamouring about her venality in getting a present out of him and playing happy families with him whilst all the time planning to break his heart…
Of course OP wants to support her son but her husband is right. Her son will fall in love again no doubt and let’s hope it’s with someone as together and lovely as OP says this girl is. Hopefully her son will have learned that he doesn’t hold all the cards and will remember she has her own mind and agency just like him.
I have a wonderful friend who very nearly missed the chance to gave children because she stayed with a man who “wasn’t ready yet” in a mostly very happy relationship for 12 years. They eventually broke up over it and she was heartbroken. Thankfully she did marry someone lovely and had a single son but because of her age it took awful losses and heartache. It still hurts her that within two years of their break up her ex was engaged and went on to marry someone else. She wanted more children and it didn’t happen.
The OP’s son’s girlfriend has done the right thing. I really hope OP can support him sympathetically without feeding a narrative of him being hard done to by his ex. He made mistakes, common mistakes, and he’ll have other chances in the future. Just not with his ex.