Why do I feel insecure about casual sex?

When I hear about a girl, who likes/wants/is have casual sex... I feel very insecure and hurt inside... ( I don't know if insecure is the correct feeling, but it's the closest way I can describe it)
(But for some reason, if she has a boyfriend I don't care, non-casual)

I have nothing against the girl seeking sex, but for some reason I feel hurt and insecure...

This might because I am a virgin, I am jealous how easy it is for women to get sex, and also my crush has slept with other guys and it hurts thinking of her with other guys...

I just don't want to feel this way,

I was listening to a story of a girl who was cheated on, and how she hooked up with "a lot!" of guys to fill the void.

Just something about the "A lot" made me feel very insecure. This hot girl may have hooked up with 3?5?10? guys? What is a lot in a week?

And I am not even at one in my 24 years on this earth :-(

I am not sure what the solution is, it's not easy for myself to get a girlfriend or sex, all I hear about is sex...

I need to stop feeling this way, can you help with your opinions?
Why do I feel insecure about casual sex?
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