How do I tell my FWB?

My friend and I have been messing around sexually for a few weeks but yesterday we had sex. It was a spontaneous thing and since it was my first time being intimate with someone other then my abuser (I was sexually abused for years by a family member and that is how I got HSV), I was not thinking about it. I’m 16 and only found out about it a few years ago. I didn’t really worry about it because I didn’t think that i would be intimate with anyone until i was in college. However, this morning I remembered that I had it and I texted him telling him that I needed to talk to him in person. I’m just really scared about what he might say or think. He knows about the abuse and everything but I don’t want him to think differently of me. We were safe and used a condom and we didn’t do foreplay so he should be safe. I’m just scared of his reaction and how I should tell him. Any advice would be helpful!