Why do I push away good guys?

I'm 19 and happen to know that a few guys have been into me recently. But I run away every time, even though they're good guys. I keep telling myself that they're not the right guys, meanwhile the guy I DO like wants nothing to do with me. What's wrong with me? Should I give these guys a chance, or would that be leading them on? I also hate the thought of settling, it makes me feel weak.
Why do I push away good guys?
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