I still have feelings for a girl, and I want to date others...

I am a 21 year old man, and this summer I was hanging out a lot with my friend (She is 19). We were in a play together and ended up spending the entire summer together. I quickly realized that I had strong feelings for her, but I knew she had a boyfriend. I ended up telling her how I felt, and she felt the same, she even said that she would break up with her boyfriend so we basically treated the situation as if we were dating.

As this continued, I quickly realized that she hadn't broken up with her boyfriend, and I talked to her about this, telling her I was comfortable being a party to her cheating. She told me that she and her boyfriend needed to "talk" before this could be finalized. I knew by now that I loved her, and I didn't want to lose her so I waited.

Long story short, I went back to school, with the promise that she would make a decision on the issue. Eventually she told me that I should date other girls, because she was "too busy with school" to make that decision. The time after that was very hard, I didn't get much sleep and I was depressed a lot, but I have gotten through the worst of it. 4 months later, and I haven't spoken to her since then, and I have met other women who I am interested in but I haven't dated anyone yet.

I realize that I can't be with this girl again, because she would probably screw me over like she was screwing her boyfriend over for the whole summer, but I am still have very strong feelings for her. I am trying to move on but I am also terrified that I will get hurt again. I guess I am looking for any advice.

TL;DR- I loved a girl, and I think she loved me too, but she stayed with her boyfriend. I am trying to move on but I still have strong feelings for her.