One of my old girlfriends had trouble cumming. Patience was the watchword. I never put pressure on her to cum. I'd ask her if "it was her turn." When it was, she'd often rub the head of my stiff prick against her clit. Then when she was ready, she'd straddle me and require a particular hip motion from me that would do the trick.

I figure she wasn't faking it, due to the amount of work it took to get there.