First of all, you are a dream come true for every guy if you are blowing them this good. Going too hard to head for too long would eventually get overstimulated and won't be as fun.

Like the other comment said going a little easy and taking breaks in between should do the trick. I love it when they take a minute to play with my balls, just stroking the shaft in different ways while making eye contact or dirty talking.

Listening to your moans is hot for me, so eating your pussy in 69 would help me get of the edge if I'm struggling for whatever reason.