OP even stated he deals with insecurity issues. It's not a buzzword at all, and that's one of the underlying factors in OP's response.

You can tell that insecurity has him comparing her fling with this guy vs. the wait to be physical with him. He acknowledges he grapples with confidence and insecurity issues. And it's important to realize when insecurities are undermining your ability to think fairly, clearly and make a rational decision.

If OP were able to go "hey, that isn't cool she did that, but I can see that she immediately hit it off with me and chose me to date, so tough shit to other guy - she chose a long term relationship with me", we probably wouldn't be reading OP's post.