I’m not sure

This is a rant/question post! So the situation is kinda bad but a week before me and my boyfriend got together I had unprotected sex which ended in the guy finishing in me. My current boyfriend knows about it! I’m not on birth control anymore because it was making my periods way too bad. Anyways my boyfriend finished in my multiple times in a week (I told him too but I wasn’t serious) I know it’s my fault if I end up pregnant but I’m worried that if I do get pregnant I won’t know which one of them is the father. Has anyone else had a situation similar?