Am I wrong for feeling the way I do?

So my boyfriend of 2 years has just told me that when he was younger him & his sister had a incest relationship, I don't know how many times but he said they were kids and he was also sexually assaulted as a kids, so I thought maybe it was because of that and the fact they were not taught right from wrong when it comes to sex.
My issue is that this is the first time in my life that someone said this to me and now that he told me i can't help but feel slightly uncomfortable yet i feel a bit bad for feeling that way because i wanted to be as supportive as possible but its not ok to me and his sister is with us almost 24/7 (I believe this only happened while they were young) so its making me feel a bit more odd, i want to tell him i feel uncomfortable with her being around so much after this new info but i don't want to come off as a bitch and make him feel bad…
Am I wrong for feeling the way I do?
Add Opinion