Please be gentle first AIBU and am perfectly willing to be told that I am but I am really reaching the end of my patience with DP's sister.
Backstory: They are very close although don't see each other very often as she lives in London and we live in the north. His Dad has many children by several women, they are from the same mum (FIL's 1st wife), and he left when she was pregnant with SIL. Only adding this so there will be no annoying drip feeding.
SIL has never and I really do mean NEVER thought I was good enough for her DBro to the point where upon first meeting she waited until he had left the room before hissing 'you had better not hurt him'.
Every time we meet she makes snide comments to me while he isn't there, previous instances have included accusing me of making up a medical condition I have suffered from as a child, criticising the home we have made together and even where I am from (the North as opposed to the South where they are from). Generally making me feel like shit.
I reached the end of my teather this weekend when we went to a party at MIL's house (MIL is lovely btw). She spent the evening being sweetness and light around DP and I (more fool me) thought she was actually making an effort and I was doing the same. However, she then began to attack my opinions on various topics of conversation, boast about her PhD in front of everyone and when I offered to be on her quiz team (they're really into that sort of thing) said loudly infront of everyone 'no you're alright I'm going to be on the smart team'.
DP then ignored me for the rest of the evening to play Go with her.
The next morning after we had left I got an earful of DP for being 'snappy' with him. I agreed and apologised for this but said that he must understand that being made to feel like shit isn't going to put me in the best of moods. Was then given the silent treatment for hours before being shouted at and told "SHE DOES NOT MAKE YOU FEEL LIKE SHIT!" and being called a liar for telling him the things she has said to me because she denies it later. I have tried just not telling him but that results in me being told to make an effort because "I love my sister and you'd better accept that". If course he loves his sister but that doesn't mean the sun shines out of her arse.
She is also needy and attention seeking and does v childish things like cheat at games that she isn't winning, lie about having bullimia and jump from being vegetarian to not so she can attract attention in restaurants.
We have apologised to each other about the argment at weekend and we don't argue a lot but when we do it seems to centre around me feeling second best and being treated badly by her. I am expected to go to her birthday dinner next month (v posh London restaurant) so I will be spending lots of money that I don't really have on feeling crap again. I love DP so so much and couldn't bear for things to be ruined for us. I am writing today because I am scared I will lose him. Please help!! and sorry about the length.