I really don't think IABU but am prepared to hear I am if that's the case.
Ds1s girlfriend doesn't like DS2s girlfriend at all, to the point where she can not stand being around her. I know this is because of DS2s girlfriend attitude towards her and a real personality clash. This has never been an issue as they both are polite to each other and never cause any problems. Now to the reason for posting...
I made plans with DD and DS1 and his girlfriend for tomorrow completely forgetting its DS2s girlfriends birthday Friday and I promised him we would do something with her as we we won't be going for the birthday meal on Friday. Can not stand her family. Originally we, that being me, DD and DS1 and Gf, was having a nice day out then going for a meal at their favourite restaurant but DS2s girlfriend is a fussy eater and won't enjoy our chosen restaurant. I said to DS1 and girlfriend today that we'll still go out together tomorrow but have to change our restaurant choice to something where DP and DS2 and his girlfriend can join. That was fine with them but DS1s gf said could she be dropped home before the meal.
That's totally fine by me, I can understand why she wouldn't want to attend seeing as she doesn't like DS2s girlfriend but when I told DP he got really angry. He has said its rude and disrespectful, she had plans with us she can't just change, she wanted to be part of our family then she has to do some things she doesnt like blah blah blah. I tried explaining to him that she doesn't like her and she has good reasons not to, we can't force her into going as she will not enjoy herself and will be uncomfortable. He's now saying if she can't find a way to like her she won't be welcome to stay over anymore and certainly if she doesn't attend the birthday meal she won't be welcome over for a long time.
DS1s girlfriend over heard and said she will come if she has too but she'd rather not and DD said they will sit together so she doesn't feel so bad being there. But I don't think she has too.
So AIBU to think that it's absolutely fine for her to dislike someone and not have to attend their birthday celebration? DP is the one being unreasonable isn't he?