Help i’m torn

I have a boyfriend who is currently incarcerated. The night before last I met up with my old high school sweetheart. It was just to catch up but there was tons of built up sexual energy because we never had sex back in high school. As a night cap we went back to my place and had great sex. I feel like shit but he wants to make this a regular thing and more. He does not know about my current relationship status. Where should I go from here?