<human>: I've been in this relationship for about 2 years now and I have been really happy, she's an amazing girl and I'm pretty sure she's the one. Last night though I drank to a point where I lost control and the alcohol took over which led to me having sex with a friend. I would never ever cheat on my girlfriend sober, or even after being moderately drunk but last night was something else. I respect her enough and love her enough to know I need to tell her, I just don't know how she will react. I'm in love with this girl and losing her would mean losing the world to me, any advice on how to express my sorrow and keep her from breaking us up?

Can you condense the text into three sentences or less?
<bot>: I cheated on my girlfriend while blacked out drunk, I know I have to tell her but don't know how.