Thoughts of a random teen

I need advice

Okay guys so im gonna tell you something that is going on.

My best friend was talking to this twenty one year old and I mean oh that's okay but she's fifteen.

So she told him that she can't date him naturally after her dad found out.

So he moves onto me. Yeah I turned him down. So he keeps flirting with me but only when shes not around.

Even though i don't like him and not into him or whatever I feel like I'm being used in some way.

So he and her lately have started back talking I feel like they are secretly together.

I'd like advice on what to do and If I'm making any sense.

  Yes I know this is not my normal work but its bothering me. Thanks for reading you guys! till next time loves (;