I suppose it's possible to lose some sensitivity because of masterbation, but in my opinion it's mostly in your head. You're training your body to respond to something that feels good. Your hand on your penis. When you first have intercourse it will feel different. It may feel better or it may feel not as good. Your body may not respond to the feeling as your used to, or it may respond better. There is really no way anyone can tell you how you'll react.
Something you can do though is to vary the way you masterbate. Try different things from time to time. Don't train your body to respond to just one method of pleasure. That way when you do "do it" it will be just another different form of pleasure. Hopefully you'll be more concerned with your partner and their feelings when the time comes though. <IMG SRC="http://www.healthboards.com/ubb/smile.gif">
Don't concern yourself over this, just about every guy does it, and yes even us married guys with normal sex lives do it. Do it when you feel like it, don't say you have to do it once a day or twice a day. Just do it when you feel like doing it.
Good luck and have fun. <IMG SRC="http://www.healthboards.com/ubb/smile.gif">
