Abuse isn't just about the sex, it is primarily about one person using their power over another person for the sake of exploiting and misusing that person. Can one 7 yo have that kind of power over another? What do kids that young understand about sex? I'm not sure.
What is clear is that you were harmed by this experience and that your friend was acting out with you things he was being forced to do with his father.
The fact that he denied everything years later doesn't mean that it didn't happen. It just means that he is ambarrassed or ashamed or else is in denial himself. It would be terribly difficult for him to admit, even to himself, that he was molested by his own father.
I hope being here on MS can help you deal with some of these issues. You are safe here. Just get used to the place and find your own pace for getting into discussions and other contacts.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)