|Masturbation does not make men go limp when they attempt sex. Most men masturbate, whether they are sexually active or not. Masturbation is very healthy.
Men often go limp before sex when they are nervous. You will probably notice that you do just fine when you are completely relaxed and comfortable with the situation whether you masturbate or not.
Llewellyn or one of the other advisers/moderaters may have more information on the health aspect of it all as I admitedly don't know the pros and cons of stopping all together. I myself still do it a few times a week even though I have a live in girlfriend that I engage with frequently.