My step son, 17, and his girlfriend had been together for almost 3 years and she had been staying over a few nights a week and was over for dinner most nights so was very involved with our family. A few weeks ago he cheated on her with a new girl at his college, when me and his dad found out from my son who is at college too we told him he had to tell his girlfriend or we would have to stop her coming over as we wasn't prepared to lie to her. He did tell her and sadly she ended things.
We then found out he had decided to have a relationship with the girl who he cheated with and today whilst we was having friends and family over for a bbq he brought her over to meet us. Everyone was super polite to her as we are not a rude family and she did seem a very nice girl but considering the circumstances they got together under I explained to him after he took her home that she is not welcome in our house and won't be welcomed into our family. This really upset him and he threw a massive tantrum about how our loyalties should be with him not his ex blah blah blah.
We have always been very relaxed about girlfriends and boyfriends coming over and we always give them a good chance before judging them but I just can't allow that. I understand I don't owe the girlfriend anything as I probably won't see her ever again but I've always tried to teach both my 3 children and my partners 2 children that respect is a huge part of relationships and even whilst discussing hypothetical situations did say I would not allow cheating in my home. If it had been the other way around and his girlfriend had been the one who cheated I would not allow her in my home either as I do not find it acceptable.
I've told him if he wants a relationship with her then i will not stop him but it won't be happening under my roof and I wish to have little to do with this new girl as I do see her as guilty as he is.