Most Helpful Guy
Think this through. You want her back. She wants you back. What's keeping you from getting back together?
The answer to that question is the fact that she's with another guy. She could easily dump him and come back to you, but she's not. She's staying with him and seeing how it goes...and guess what, if it goes south, whose gonna be there to clean up the mess? You.
First off, there is no such thing as a "break." I realized this after my fiancé of 2 years (dated for 8) requested a break, told me she'd stay committed, then cheated on me. Its not a break. Its a breakup. Use that as a learning experience.
Secondly, how are you okay with wanting to take a girl back who you know got drunk and hooked up with another dude in between your relationship? She's been with another guy while you're sitting home on the computer asking for advice man...she doesn't care about you. She has someone new, and she obviously didn't have too strong of feelings for you when you were together considering she's with another guy only a week and a half after your break. Now, she's lying through her teeth and stringing you along.
Your need to accept the break up. They're tough. Stay strong. She is one of 3.6 billion women on the planet, and I guarantee you there is someone out there who wouldn't toy with your feelings like she is. You have to cut her out of your life. Leave hers completely. Put away everything that reminds you of her. It'll take months to completely feel better, but its a breakup. Its tough. But you'll see later in life, that any good woman would not do this to you.
Step 1: Cut off all contact...phones, Facebook, everything. Don't even owe her an explanation
Step 2: Grieve...mourn...take time for yourself. Do things you enjoy to distract yourself. Confide in friends if necessary. This starts the moving on process
Step 3: Focus on yourself...join a gym...focus on your goals...build yourself up and improve your life.
Step 4: Once you're happy and secure with yourself, slowly introduce yourself to the dating world again, and use this mess of a girlfriend as a learning experience.
What qualifies me to tell you this? As I said above, I was once engaged. She cheated on me with 13 men. I wanted to take her back because I loved her. Instead of doing what was best for "us," I did what was best for me and I refused to take her back, even after she called crying on a nightly basis. I cried for months as well, but it was worth it.
I sincerely hope you don't get back with this girl. I hope you refuse her a relationship with you, and refuse her a friendship. She doesn't deserve it, and you deserve to be the one to come out on top in this situation. Take your answerers' advice and you will.