My younger sister bumped into my ex boyfriend at a party, said she fancies him, said I’ve moved on, so it’s no problem to date him right? I feel surprisingly upset about it and have never dealt with this before. I know it’s not a crime to date a siblings ex; it happens, many would have no problem, but it feels upsetting to me. She is criticising me for being “possessive and sad”, accused me of still having feelings for him (I don’t in that way, just fond memories) and is calling me jealous. He just wrote me an email also calling me sad and why can’t I just let her be happy. It feels like a gang up and I’m in the way, and I’m getting a lot of criticism, although I haven’t said much. I just haven’t given an enthusiastic green light. They’ll go for it anyway, I think. I’m a new relationship and fairly happy in it, I just feel ick at a guy getting a chance to compare us sexually, and feel a bit thrown under the bus by my (ultra competitive) sister. AIBU?