What should I should do?

So, I've been good friends with this guy for like 3 years, & his girlfriend is one of my best friends. A few weeks ago me & the guy were hanging out, just me and him, & we were pretty high & he told me how his girlfriend had recently given him permission to f--k around with other girls, like just casual (she told me a few days later herself that she did). And he basically asked me if I wanted to be f--k buddies with him. I've always been just friends with this guy, & I know in the past he was interesting in dating me but I'd always wanted to keep it just platonic with him. So I told him I'd have to take a rain-check on that one. He asked me if 'rain-check' meant "not now" or "never" & I did tell him it meant "never" cuz at the time I felt awkward about his question, not to mention the fact that his girlfriend might get just a liittle ticked if she ever found out (she DID give him permission to hook up with other girls, but she told me that she's be really sad if he actually chose to. And I don't think it would help if she found out it was me he was doing that with..) He told me that if it did happen, he wouldn’t tell her it was me, but I still vetoed the idea. But lately I sorta changed my mind and I’ve been a little tempted to text him & ask him if he still wants to. The only thing that’s making me hesitate is that I’m a virgin & I wanna lose it but & idk if I’d be completely comfortable with it or not. Also, I’m not on the Pill & I’m not sure if I trust just using condoms either lol. What do you think I should do?