he doesn't CUM

So my guy is the best lover I've ever had hands down can make me cum multiple times in a row and always makes sure I do. I KNOW he's very attracted to me. but even from the first time we've hooked up he's had issues cuming . sometimes he doesn't at all! it makes me feel bad , I've asked if I'm the issue he says no. he usually can cum with oral but takes for ever it's exhausting ! I'm Talk I g like hours to make him cum. I should add he does drink a lot and uses coke from time to time . but still I need answers .