<human>: First off I'm sorry if this is in the wrong place but i just needed to get this off of my chest. 

So around 3 months ago, this girl and i started hitting it off (her 17, myself 16) it started with us going to a party and from there we've talked almost every day and ended up with me going to grad with her. We talked about making what we have "official" and she said she wants to wait until she's finished exams. Which is right around now..

So everything is going great except that on monday night i was out getting something to eat, and i get this text from another girl that I'm really good friends with (she's 17) saying how she was really bored and wanted to do something after she was done work, i suggest a movie and meet her at her work. We get there a bit early and talk until the movie starts, now near the end of the movie she starts touching my arm and trying to hold my hand which i pull away from, then she leans over and cuddles with me, then it ends. We get in my car to drive home and we hardly talk on the way home since its getting late. When i pulled up on her driveway she leans over and gives me a hug which wasn't out of the normal but then she pulls away and starts kissing me to which I'm in total shock with and then she left. 

So now I'm not sure where I'm at, i had a crush on this girl a while ago, and i feel really terrible about doing this behind my (soon to be) girlfriends back.. 
Help me out Reddit, i need some advice.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Made out with a good friend behind the back of my soon to be girlfriend. Feel terrible and don't know what to do..