I agree with ^^above posters. I'm sorry but you don't seem to be as sincerely upset about your past affairs or your partner's feelings. It seems that you are most worried about getting caught...which implies that your true concern is how him finding out will effect you. There is no room for this kind of selfishness in a relationship. Come clean and face the music..or cut him lose and be single if you want to sleep around. I think you need to grow up a bit more and do some soul searching about your values before being in a committed relationship. I don't know how old you are..but your emotional maturity seems to be young... which to me says..you are probably young as well. So I think it might be time to let this guy go..be alone and work on getting to know you...then who knows what the future holds?..I'm sure once you figure out what you truly want you will find it.
And for some people that is not always monogamy..but there are others out there who are open to that lifestyle..most important is that whatever you decide..keep it above board!..secrets don't work in any relationship worth having.
-LITW