My sister is dating my cousin, is it OK for me to feel uncomfortable?

Anonymous
I'm 21, my sister is 25 and my cousin is 23. I know my cousin has liked my sister for a long time (in fact, quite a few of our cousins have liked my sister) but yesterday he wanted to talk to me about this and he confessed that he has never felt this way about any other girl, even his last 2 girlfriends with whom he had long-term serious relationships with. But during all this time my sister didn't like him romantically at all. He also said he has fallen in love with my sister. But just the thought of them 2 makes me uncomfortable.

We went on holiday a couple of weeks ago (me, my sister, my cousin and 2 other girl cousins) and my cousin kept making it obvious that he wanted my sister. Then the night before our flight him and my sister had a really long talk and he confessed he was falling in love with her. On that same night they kissed after a night out of clubbing. They were both drunk and my sister said that's why she kissed him back. I didn't know whether to believe it or not. Then at the airport, him and my sister were having a really long talk again and my sister told me she really likes him.

The thing that makes me mad is that my sister has been saying so much bad stuff about my cousin. Stuff like him being a sleazebag, he's too desperate and needy, he's so insecure and a cheat etc. She told me she recognized all this stuff when she was helping him get over a really bad break-up with his ex-girlfriend. And now she tells me after letting him explain about everything that has happened to him she understands. And she says nobody has seen his romantic side. He had a romantic side when he was with his ex-girlfriend yet he still cheated.

Anyway, they say they are going to tell the whole family soon because now my sister is falling in love with him also (all it took was 2 days, wtf!). She also says she can see herself marrying my cousin. The thought of my cousin and sister having sex makes me sick. I just hope it doesn't cause any problems with families, especially if the relationship doesn't work out. And when all our friends find out too everyone will be talking and gossipping. But I told my sister it's making me uncomfortable and she says I just need to get over it (which is true I guess). But I don't see cousins dating each other as normal, is it right for me to feel uncomfortable? Or should I just suck it up and accept it?
Updates
+1 y
They haven't had sex yet, just kissing/making out. But from the sounds of it they are both in love with each other so if the relationship goes far enough then they will end up having sex.
My sister is dating my cousin, is it OK for me to feel uncomfortable?
12 Opinion