kegles- exercise of the PC muscle. Will allow you to control things a little better. Till then your best bet is to think about your grandma naked or something else gross to ward it off.
You could also try changing it up. When you're about to cum, slow it down, or change it up. Keep her going if you can (you have more than one appendage capable of stimulating pleasure) until you've calmed yourself down a bit. Then dive back in for more. She'll appreciate you taking the time, and not just getting off. There is a technique and a rhythm to it, and once you learn it you'll be able to control yourself for hours if needed.
|