I think Miz Cleo (the psychic) is in jail now...at any rate, we don't currently employ a psychic at this time.
Seriously though...you've asked a question that is impossible to answer. Sex does different things to different relationships. It varies from couple to couple and situation to situation. So will becoming sexually active have some affect on your relationship? Yeah, quite likely it will. Will that affect be positive or negative? Yes, no, maybe...who knows?
I'd suggest you check out some of the articles here on the site:
Ready or Not? The Readiness Checklist
First Intercourse 101
Safe, Sound & Sexy : A Safer Sex How-To
Then think about your relationshp and where you are personally in your life right now. You are the only one who can decide whether or not now is the time for you to be sexually active.