So I'm 23, straight, male. I've been dating this girl for about 2 months. My old best friend from freshman year of college (I only went to that school freshman year) came into town for one night and crashed with me. He's 24 and gay. We used to be really close friends so we've hooked up before and had sex quite a few times but I'd never do that with anyone else. So he's staying with me for one night and sleeping on the same bed. We go to sleep one night, wearing only boxers. While I fall asleep, I wake up to him grabbing my ass. I didn't mind it, so I went back to sleep. I woke up again and my boxers are off and I feel something between my ass cheeks. I realize that he's got his hard penis in between my butt cheeks and his hand squeezing my ass. The convo went sort like: (whispering) "What are you doing?" "Just getting comfortable." He starts poking my asshole. "You know I have a girlfriend..." "That hasn't stopped us before." "I don't know if we should..." "Don't you miss our sex?" "You know I do, but I don't know if we should do this..." "A few strokes won't hurt." He starts kissing my neck, he knows I love that. I let him lick my neck for a while and ask him "do you have any lube?" He grabs the lube and slowly slides it in. I say "go slow, baby. It's been so long." "Have you been letting other guys in here?" "You know this is only yours." He starts stroking harder and all I'm doing is moaning and whispering "daddy" while he constantly says things like "I've missed you so much" and "I love you". I hadn't had him inside of me in so long and it felt good to feel his hands grab my ass and spank me while he gets deep inside of me and makes me moan so good. I told him "I've missed your dick so much, daddy. You know this will always be yours." After he finished, he gets on top and we start making out. He went down on me and gave me head until I finished. We fell asleep quickly after that and he left the next morning, everything normal. Should I tell my girlfriend about this or should I just not bring it up?