hanging,
First, and foremost, know that you're only 21! What's that mean?!? You have your whole life (and plenty of women) to fix this problem. There's no rush
Let me ask you a few questions before I give my diagnosis:
How often, on average, do you masturbate and ejaculate a week?
Do you always ejaculate?
Do you think about ejaculating (i.e. want to/ fear to/ don't want to) prior to and during sex? How about during masturbation?
Do you have a gf? Long-term? Short-term?
As a person that has dealt with this problem, I know exactly what you're going through -- so don't feel alone! Know that it is conquerable -- especially with the right techniques.