First time I did it was by accident. My ex and I were doing a MMF with my best friend. We all had been drinking and wound up in bed together again. We had done the threesome before, just never man on man stuff.
The two of them were on their side and he was fucking her from behind. She wanted me to eat her pussy which I always loved to do. When I got down there I could see he was fucking her and I didn't want to do anything. She pushed my head back down and I started to lick her.
Whether she did the next thing on purpose or not, I don't know. His cock slid out and ran across my tongue. Someone put it back in her pussy. A few minutes later, it happened again. It didn't really bother me either time. I was having fun eating pussy.
When it happened the third time, I said to myself, shit, I'm just going to suck his cock. I never planned on it, I just decided to do it. I grabbed it and started sucking. I had never even touched one before (except my own of course) let alone suck one. I knew what I liked so I just did it to him.
All of a sudden his cock swelled up and he started pumping cum into my mouth. I didn't think twice. I just swallowed every drop. Then I milked it dry. He started getting soft and I realized what I had just done. I figured our friendship was toast. I was embarrassed, but not remorseful. In fact I decided that I really enjoyed it.
He and I briefly talked about it afterward. Funny thing is I did it again to him a few more times in a MMF situation and twice where it was just the two of us. I guess I was pretty good at giving head because he asked me to do him a couple of times. We all stayed friends until his unexpected death at an early age.