Im a 25 yr old male and i'm attracted to my 17yr old cousin. We are only related by marriage so it's not like we are real cousins. We hang out a lot and go on "dates" although we have never done anything sexual. Regardless I can't stop thinking about her.
Take her home, and shag her rotten.
Why do you need a bunch of saddo internet fuckwits to tell you what's staring you in the face?
And once you've done it, come back and tell us what it was like. Huuhuhhuhrrr!
If you do get sexually involved with her, and if there's a break-up down the road, you will still have to see her at family functions, which could be very awkward.