I've never had any male masturbation buddies. Only few female friends were masturbation buddies. My first was when she and I were teens. Oddly enough we never had sex with each other until we were in our early 30's.
In my 20s I had a friend who slept over in my apartment. We watched each other masturbate for a few years. On a few occasions it went a bit further. He would rub my cock and I'd rub his. We had oral sex a few times and swallowed cum.