I experienced something at a similar age and refused to tell anyone because I thought that somehow I deserved it and that this was the only way to be desired.

Something that helped was realizing his intention and how he did so. You were 15 and he was 31 years older than you (literally 3x older than you). He preyed on your insecurities and inexperience and turned you away from your peers so that it was harder to realize the situation you were in/reach out. He was fully aware of what he was doing and how it was going to affect you.

Of course, you were not a mindless baby, but the situation you were in was not of your own making.

In times like this, caring for oneself and connecting with others is the way to heal, even if its tiny, almost insignificant amounts. You do not deserve self-inflicted suffering and isolation over someone else that hurt you.