Long back story but briefly my DD caught my DS's girlfriend cheating on him at a party and so told him. GF went ballistic at being caught out and went on to make DD's life absolute hell for the next 18 months, completely ruining her whole Year 11 at school. We're from a small town and gf was in the 'popular' group at school and was very powerful and manipulative, made up lies and rumours and turned lots of people against DD. Really nasty bullying but gf turns on the tears and plays the victim when confronted and seems to get away with it. DS remained besotted with gf, refused to believe she had cheated despite lots of other witnesses and playing down the bullying as if it was nothing, he seemed almost brainwashed by her. As you can imagine this caused a lot of friction in our family and I was stuck between the two of them. GF treated him really badly but he still wouldn't break up with her and then thankfully she broke up with him, he went to uni and I hoped that would be the end of it. This was all over three years ago.. DD is now at uni and DS has moved to a city for work. GF still lives here and so DD tends to bump into her if she's here in the holidays - GF still goes out of her way to make comments/give nasty looks to DD. Out of the blue the other evening DS phones DD and says he's seeing this girl again, they've started talking and she's spending the weekend with him. DD is very upset and feels completely betrayed by DS who she is really close to. I have to agree with her. I have a really good relationship with both my kids and don't feel it's my place to tell my son what or what not to do but can't believe that the fact ex gf bullied his sister so horribly would put him off her. Can't believe this is all surfacing again. I feel completely on my daughters side in this - AIBU?