This guy is begging me to do him what should i do?

so he is coming over after work. He and his girl wanted to have a with me but i told them I am straight and I don't like girls. The girl friend gave her bf permission to have with me. I am really tempted because I haven't had in a while but then on the other hand I want to say no because I will feel like a skank. so please help what should I do??