My best friend (who's married) keeps touching me, How do I handle this?

I'm currently living with my best friend (and his wife) and in the past, I Had a massive crush on him. We recently talked about it, about how I felt, and he was really good with it. If anything, it's made us closer. So...the other day, we were messing around on the couch, having rough play, pinning each other down (as boys do) but he suddenly reached out and touched the tip of my dick (I was only wearing little tighty whities, so it left nothing to the imagination) He rubbed it for a few seconds, and then he put his head down and sniffed my crotch....then he looked at me to see my reaction. I was paralysed with fear, I just kept thinking, "He's now a married guy! this isnt right!" But I didn't stop him, he was quite preoccupied with watching my dick getting hard. I know it's immoral, but I can't help but love it. What should I do from here? I don't want to ruin his marriage, but he insists it doesn't affect anything.