You've made a complete tit of yourself but I'm not sure you see it yet, despite the overwhelming majority and your own son telling you so. Sit back, take a breath.
At the risk of making assumptions, when you and your son's father bought your first house together, did you contribute a full 50% financially? Given the way the world has typically worked I'd hazard a guess that's very unlikely. Did you - or your husband - consider the house any less your home for that? I really hope not because that would have been a very unpleasant attitude.
You have a small but distinct opportunity to fix this. Probably best to delete the original post and do a new, far more reasonable and less cringy post congratulating the couple on their new home. No-one cares about the financial details. This might go some way towards showing them that you appreciate you made an error earlier.
From this point you can decide whether their marriage means you gain a daughter or you lose a son. For whatever reason you don't seem keen on her but it's in your own best interests (and your son's) to make an effort to build a good relationship with her. Try and lose the attitude because the fact is that your son has chosen her. He will marry her, support her and (if he's a decent man) put her first before you and anyone else. That's what the saying 'a son's a son until he takes a wife' is about. As upsetting as it may be, you are no longer and never again will be the most important person in his life. She is. Your opinion on his finances or anything else in life is largely irrelevant, but what she thinks will matter very much to him.
Alternatively you can dig your heels in, keep on being the MIL from hell and find you don't have the relationship you would like with your son and his family in the future. Swallow your pride.
Oh, and in future don't post on AIBU if all you're really looking for is an echo chamber.