Technoviking...you're not the first guy to think that his sweetheart was "different from most women" and that "she'd NEVER do _____ or______ to me"
Cutting right to the chase, she's showing her true inner skank right now...the scandalous ho tendencies she successfully hid from you long enough to get you to take the bait and marry her.
It happens. Can't spin your wheels looking for answers...put all that energy into moving on.