I agree he was totally out of line asking you for a BJ! Dont assume all men are like that Lisa, some of us are gentlemen. Anyway, as far as telling you g/f, thats a tough call. Unless you think it could happen agian, I dont know if you should say anything. She might not trust you going out again. It might be wise to let sleeping dogs lie, and leave it in the past.
BTW, I do agree with Tachi and Foxy that its best to be honest, but this sounds to me like it could've been a one time thing, and why hurt your g/f if you dont have to.