Theres nothing you can do. Its only half a relationship, if he doesnt like you back. So pick up your chin, and move on.
I know its easier said than done, but dont let this guy cause you to be down and sorrowful. Move on and find someone who likes you back. Life IS short.
Mick
*edit*
PS If you are afraid of him liking your cousin, it suggests to me you have seen your cousin with him and being playful/flirty. If this is true, then I wouldnt be asking her to "get the goss" because she'll have a biased opinion.
*MaJiK*
There are not many things I fear in life, but disappointing you is my greatest.
I love you even with your flaws... I love you because of your flaws.