OMG - My girlfriend's boyfriend fucked

I was visiting my girlfriend, she wanted to buy a pair of drinks and I was in the shower. Without warning, her bloke came into the bath looking for his girlfriend, but then suddenly he wanted to get into the shower with me. Unbelievable, he didn't care about his girlfriend at all. Since I was also so horny, it just happened! I don't know how I could have done that. I just hope my girlfriend doesn't find out about it. Would you have joined me in the shower too?