Please consider using more reliable birth control than the “pull out method”. Please protect yourself from STDs as well. As far as the betrayed girlfriend, it is sad but since you have no intention of telling her about your experiences with her boyfriend, I think the only thing you can do is move on and continue not responding or contacting the man involved. Also, I don’t know how close you are with this friend of his, but unless he’s a good friend of yours as well I would consider limiting time with him as well to remove yourself completely from this drama.