HELP should i tell him...?

I have been talking to this guy for about a month and a half, we work together, we have hung out, made out, and we talk about how we like each other...we kind of have a thing but we never talk about what we are exactly (which im fine with). BUT last night I got reallly drunk and hooked up with one of my good guy friends. Should I tell the other guy that I hooked up with someone else or should i just let it go since we arent dating???