Dear James

When you dream about a cousin in your dreams it most likely to be a displaced version of yourself, or a close relative of yourself but distant enough to enable you to maintain a detached perspective.
If we dream about having sex with someone famous, even our next-door-neighbour, or in your case your cousin, it's often some quality in him or her that we desire rather than actual sex or intimacy with that person.
This dream indicates that you need to take a look at yourself and your relationship circumstances in a more objective manner.
You should look at the qualities and what you find attractive to your cousin and this should give you the key to what you are looking for when seeking a partner.