advice please... I don't know how to feel right now..

I don't know how to make this story short but I will do my best. I was with this guy for five years. It got to the point where it was very unhealthy (both physically and emotionally) so I left about a month into college. Main reason being I could just tell that I wasn't making him happy, in fact just me being around him made him like aggravated. I thought I could do it but I thought about him every day and night. I missed him so much and I found myself just getting high all the time to stop me from thinking about him. I tried to reach out to him a few times but he never responded. He is very close with my family and he talked/ would hang out with them so I always checked in just to see how he was doing. I've been studying abroad so he started talking to me a couple of weeks ago through skype. We're trying to build a friendship and we were kind of trying to figure out what we could be so finally I just asked him do you think we could ever be together again (because he's honestly all I want I push everyone else away because no one will ever be what he was to me, my best friend all through middle and high school.. he was just always by my side 24/7) he told me that he couldn't put me throug this and I wasn't understanding until finally he told me he was with a girl for about two weeks and she gave him an STD and then left. I was shocked and started balling my eyes out. I couldn't breathe I have such a headache and I don't know what to do or think. I feel like it's my fault for leaving in the first place. And I still love him, I still want to be with him... I just don't know what to do or think... 😔