I found out my girlfriend is my cousin
How do you feel about dating your cousin?
It makes me feel uncomfortable.
You should feel uncomfortable dating your cousin since it is unacceptable to do so. Instead of dating your cousin you should date someone who you are not related to.
Okay, I am going to end the relationship and let her know why.
That is a great idea. It is unacceptable to date your cousin and since you now know, you can break up with her without feeling bad.