My boyfriend thought it was funny to dry hump his sister?

Anonymous
I went to my boyfriends house for the weekend for the first time and he behaved extremely weird with his younger sister. He gets too touchy with her (will randomly pinch her butt or boob) and when we went outside, he dry humped her and they laughed! Then the next day he sucked her cheek to the point where he left her a hickey looking mark. & seriously when I asked him why he does that, he got mad and told me they joke around like that. I couldn't wait to get out of there. As far as I know, no brother and sister should have a weird relationship like that. But for them it's normal. Honestly, do any of you think there could be some strange incest thing going on between them? Because I sure as hell don't think that's normal.. He has all these random selfies of his sister saved on his phone. Can someone explain to me?
Updates
+1 y
So I told him my concerns and he said I am dumb for even thinking of it "sexually" because that's his little sister. Oh well. I'm not going to be a part of some strange brother/sister relationship. Thank you all for your opinions! I knew I wasn't over reacting!
My boyfriend thought it was funny to dry hump his sister?
40 Opinion