You don't.
How do i tell my cousin that im deeply in love with her?
I wouldn't.
I have always had a puppy dog secret crush on my husbands cousin.... The key word is SECRET! Some things you just don't let out of the bag!
I'm sorry, but in this society, you just don't. It won't result in anything, and for the best, should not result in anything. Distance yourself and you'll find someone else. Some things in life are just hit or miss, and this happens to be a relative, so it's a miss!