Oh, honey, I have been there! My son had a girlfriend, I took her in like my own. I drove her to work, I cared for her, I gave her clothes and encouragement. I helped her with her schooling and she lied to me about graduating after I spent hundreds of dollars on prom attire, grad gifts, etc. The relationship was volatile and eventually she left my house.
Won't lie, I still love her like my own, but I don't love the things she did.
As for the boys, yours and mine....they can climb the fuck off their high horses as far as I'm concerned. it's not about taking sides. It's not kindergarten. They brought these ladies home. They asked us to fold them into the family. They should be pleased they have mothers who are so loving and accepting. But like you, no other girlfriend got her feet under my table.
In the meantime, you tell that boy from me, he needs to pull his head out of his ass.