My girlfriend broke up with me and now she's flirting with another guy less than a week later?!

So I've been trying to get over my girlfriend who recently broke up with me/try to get back together with her at some point in time? There are a lot of factors that made this breakup so complicated. I need straight answers because all my advice I've heard have been from mutual friends so of course they're going to be nice towards me and her.

By the way, I'm 18 and she's 19. We both go to the same college and live very close to each other at college, not at our actual homes, and our friends places at college and we see each other a lot.

Things you should know:

- She broke up with her last boyfriend after she and I had been flirting for about a month first year of college.

- She met this 25 year old guy, we'll pretend his name is Jim, near the end of summer and now they're "best friends."

- They've been to movies together, she's hung out at his house until midnight, and they text each other all the time.

- Around the same time she became friends with Jim, she started becoming less interested in our conversations but claimed it was because she was tired from her volunteer job.

So what happened was that one night I had a talk with her. I wanted there to be communication between us because I knew that's what's needed in order for there to be a strong relationship. I decided to be honest with my feelings and asked her if there was anything going on between her and Jim. She said no and proceeded to become a little angered at the fact I didn't trust her 100%. She said she needed some time and space so I did so. 3 days later we went on a walk and had a talk about how I wasn't being her friend anymore and that it was affecting our relationship. She even went to ask if I wanted it "to be a 1 person relationship" because she didn't have that spark anymore whenever she saw me. So we broke up that day but she said that she still loved me and whatnot.

I tried not to see her and tried to move on but it's hard seeing as how we lived very close to each other and saw each other everyday unavoidably. 2 days after the breakup, we were at our friends house hanging out when suddenly my ex leaves and comes back with Jim. She then proceeds to flirt with him occasionally throughout the night in front of me. Eventually I couldn't take it and said that I wasn't feeling well and went back to my house. Apparently he was invited over for the weekend to hang out with her and throughout the weekend, anytime I hung out with our mutual friends when they were around, I'd see her flirting with him.

She was my first serious relationship and I really miss her as my girlfriend. I know she wants to be friends still, but how can I even start to rebuild that friendship with her when all I see right now is her laughing it up with Jim and avoiding having to talk to me, let alone our friends even.
+1 y
Update: link

Potentially viable thought?
My girlfriend broke up with me and now she's flirting with another guy less than a week later?!
Add Opinion