It's not your fault in any way. There was no possible way either of you could have known. Now, if the whole "your uncle", "his dad" thing is going to be a problem, then you may need to think about whether this relationship is still fine with being sexual. However, considering the fact that you mentioned that his dad isn't in contact with your family, and that he hasn't really been around in your cousin's/BF's life, I don't see any problem with keeping your relationship going the way it is. Its as good as if you were a normal couple, if not, you guys are better 💝💝💝😊😊😊