What you are describing most certainly is rape. Do not allow yourself to be alone with this man.

Do you think you could tell your cousin that this uncle has gotten inappropriate with you - to put it mildly? You don't have to reveal the extent of his attack, if you'd rather not. Is your sister old enough that you could tell her?

Not wanting to lose your relationship with persons you love is understandable, but you must not risk being attacked again. He will interpret your willingness to be around him as a kind of consent to his advances. This kind of behavior tends to escalate. You are probably not the only young woman that he has victimized.

You don't need to feel guilty. You do need to protect yourself. You are not obligated to "press charges against him." Beware of thinking that you know for sure what is best for your aunt and cousin.

What you've experienced is horrifying.