Luke, that sounds like he was really thick. I've deepthroat a few cocks that were very long but thin and was sort of able to breathe, but if he's thick, then his cock will vapourlock in your throat once it's past the gag reflex, so you basically have to hold your breath, plunge down on it, stay down as long as you can, then come up gasping for air, then go down again. This is why deepthroating is such a feat. It takes a lot out of you. The good news is, a lot of guys are really turned on by just watching someone work so hard to pleasure them, in addition to the nice feeling.