[Serious] How do I apologize to a woman after a hook up?

So first of, I'm an 18year old male I fucked up big time We made a pause, because she's not yet sure if she wants to get in a serious relationship with me. During this pause she went to England to visit a friend, and I thought it was already over, I was heartbroken. Last weekend I was drunk as hell and had sexual intercourse with a random girl. Later on, my girl came back from England and she wanted to see me, so I went to see her and she asked me what I did last weekend. I lied to her, didn't tell her what I did. That random girl I had intercourse with is a friend of the best friend of my girl. She told her, and she confronted me with that this weekend when I went out. She said we'll talk next week (this wednesday) and I told her I'll bring her a solution. She was all dissapointed and I feel so dumb for it. Literally the most stupid thing I've ever done. How can I apologise? What would you women want a guy to do if that happened? Of course all trust is now gone, so how do i rebuild..

Thanks for your help in advance

TL;DR I hooked up with a girl and she found out, and I didn't tell her afterwards she asked me what happened on the day of the hook up, I lied to her.

/r/AskReddit Thread