Depends, Are they together?
If not, talk to your cousin and find out if their is anything there, and if not ask them would it bother them if you decided to screw her. I mean you do not want any problems with your family so that is my opinion, and that is what I would do.. But whatever you do Best of luck!
Yes, then call up your cousin and brag about it. That way you can **** them both over.