I think I'm in love with my cousin.
What makes you think you're in love with your cousin?
When I think of him, I feel good
Attraction is complicated, but you should stop yourself from acting on a attraction to a relative. If things go wrong you will still have to see them in family reunions.
I'm going to tell him how I feel, I don't care if it's inappropriate and illegal
If you tell him how you feel, it will be extremely awkward, possibly for the rest of your life. You'll be much better off spending time finding someone more appropriate to date, instead of a cousin.