<human>: Give me the gist of the text in a nutshell

So, recently discovered that my friend and I have feelings for each other. It started when we were on a night out and we began getting closer (PG style). 

I guess we played with fire, when I wanted to a watch a movie and there was some flirting. We watched the movie in the office after work. We ended up holding hands, he said he liked me and we ended up kissing.

He said he wants to break up with his girlfriend. When they talked, she begged him to love her the way he did before (they've been together for less than 3 months) and said she was a great girlfriend... I knew she had cheated on him with another friend of mine. And my face winced and gave it away. So he now knows she slept with his friend two months ago.

He spent a couple of nights at mine but we didn't sleep together. Then yesterday whilst I was working a night shift he slept with her. I feel sick. He said he doesn't feel guilty when he is with me, but feels guilty with her. Said he was thinking of me when he was with her.

Should I forget him? I feel sad. I have to see him in the office all of today. Should I say something to him. I want to cry. I have no one to talk to about this.
<bot>: Started to have feelings for someone with a girlfriend. Spent time with me, when I'm at work he sleeps with her. Says he was thinking of me. Feel sick.