While trying to get a hold of it, do you think of the next day's races or fight not to fall asleep? Know how to react. Clearly, a good discussion is needed. If your parts of legs in the air become calvary, it is high time to fix it!
Rather than prolong the penetration more than reason, go for more preliminaries. Playful, sensual, exciting: everyone will find his account. Also vary the positions, the Kama-sutra still has a lot of pleasure to make you discover. Feel free to imagine naughty scenarios or use sex toys : effects guaranteed.
To summarize, when the sex becomes boring and that the pleasure is too much to wait for you to take the bull by the horns!