How would you feel about this?

Okay, this could seem confusing, but I will try to explain. My boyfriends sister is moving to where we live with her family to find better work. Well she has 3 kids and one on the way by a different guy from the rest. Well, her oldest really didn't want to leave (she's 15) and come over here, so she made up something about my boyfriend...she told dfaxs(child services) that my boyfriend made her suck his when she was 5. He would have been 10. His mom wanted me to ask him a/t it because she was kinda scared to ask. Anyways I said something and he got really upset and said I would never do that. He said when we were little we played touchy grabby, and I've always felt bad about us being touchy and grabby, but we were kids and I would never do anything like that. He said it was gross of him to be like that with her when they were kids, but I know that I used to do stuff like that with my cousins and I just p it off as exploration. Especially since it was nothing major. Anyways.