Possible incest

I need help. So my daughter’s father has never really been around. He met her when she was 8 months then left after 5 and hasn’t really been consistent. He moved states at the beginning of the year and it was alerting to the family because there was a rumor that he was dating the cousin he moved with( his mom’s sister’s daughter). Anywho, he came back this month and said he was going to move back then changed his mind and I guess he’s moving back with her. I brought my suspicions to his sister that they have a relationship or something going on and she confirmed that it is true. Other cousins, who they ( bd n his presumed cousin gf) lived with, also had these suspicions. I don’t want to believe it is true but multiple saying/thinking this feels like it is. My issue is that I don’t know if I am being dramatic or overreacting but I don’t want him in our lives because 1) how do I know he won’t try something with our daughter and 2) I feel that is just embarrassing and my daughter shouldn’t know about that but i’m not sure if this is the right decision. As I said, he hasn’t really been around so I don’t think it’ll be an issue cutting him off but the thing is what do I tell my daughter when she asks about her dad? Idk what are your opinions

also to add: when i first heard it i asked him and he was like “ no that’s a weird question why are you asking this” and then he started mocking me like ask me again then so idk if to believe him or not.. also when he came around we did have something going on but it fell apart during the summer when she got here so i’m not sure if that had aomething to do with it as well