What some people said is true--- it's all in your head. At least it was for me. All I was thinking about is, "I want to have an cllmax", "I hope I have an cllmax", "oh there it is"...and there it wasn't.
Women need physical and mental stimulation to cllmax. We need to feel and be aroused. The best way to kill arousal is to think about something that isn't in the moment. Instead of thinking about whether or not you'll cllmax..think about how sexy your partner is, how good you feel, how great the sex you're having is.
Get into the moment as much as possible, relax and let it cum!