<human>: Can you give me the gist of the text in a nutshell?

I made the biggest mistake of my life about a month ago. An old friend of mine from highschool started texting me randomly, and things got sexual (texting plus a few pictures) the next day, I cut contact with her and deleted everything. Earlier today I summoned enough willpower to talk about it with GF. 

She was absolutely devastated, which breaks my heart. It may be hard for some to believe, but I love this girl. I want to be with her for the rest of my life, and I can't believe I fucked up so badly. I will never, ever do anything to hurt her ever again. I know that this is going to be a long road ahead of us, and I'm wondering what things I should keep in mind to help her heal and rebuild her trust in me.
<bot>: I was a piece of shit and cheated on my girlfriend, but we want to work through it. How can I help our relationship survive?