TBH, OP, you don't really sound ready to be married. Maybe get into some talk therapy to cleanse your present of your past (since you mentioned having been cheated on twice just in this brief question). It's never fair to drag your history into a current relationship. But that said, don't marry someone you distrust this much. She may be entirely innocent and you may be out of your mind, who knows. You just can't blindly tie the knot here when you've got all this unresolved angst from the past AND you also think your betrothed might be cheating on you. Good luck.