I am my fiance's first relationship and first everything, just like here. We started dating senior year of college (we're mid twenties now) so the timing is a bit different but I totally understand your fears. I had my fair share of relationships before we started dating and I had similar fears (especially about pacing). I decided after a few dates that I truly liked him and so whatever pace he was comfortable with would be our pace. I made sure to emphasize the necessity of open and honest communication in a relationship. And I also addresses every time he began to put me on a pedestal, reminded him that I am a real person with flaws and relationships will get hard at time event though everything had been perfect so far.

Communication is key. As long as you're both honestly and timely communicating your hopes and expectations, if you are compatible everything will work out.

I am now thankful that my fiancé doesn't have any baggage from past relationships, no exes, no bad habits carried over, no "one that got away" etc. I never felt that we went too slow or his past took away from my experience in any way. I would say relax, give it a chance, be proactive about communicating, and good luck!