Holy shit... women have multiple partners too? For shame! Wow... there were 5 guys before you came along... Damn, I guess not all women are virgins... Get over it... Women make mistakes, go through trial and errors... they will have "ex's" just like guys... Imagine that, men and women having so much in common..
You didn't think all 15 of the girls you've been with were virgins too.. did you? I think you need to get down off your high horse and accept the fact that people will have slept with other people before being with you... that's just a fact of life, get over it.
This is called a "non-issue"... in that it is expected and unavoidable... reserve your insecurities for something far more devastating than 'oh my god, she's slept with others before me.'
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen