I could write a novel on this. Sooo... I started dating this girl in high school, and then we ended up going to the same uni. The first time we broke up was because of an incident that happened in the student union during dinner of fall break. We were fighting and she was pissed at me and sent me a text that said "we're over" and so I just said "okay fine". She then continued to apologize and say we weren't and needed to talk, so I walked over to her dorm and we continued to get in a giant fight outside of her dorm that ended with me breaking up with her and her crying and screaming at me. Though I felt bad, this was the right thing to do. I had been having doubts for a long time, but she always convinced me that it was because I wasn't trying or didn't care enough, and that it would completely work out if I did. Fast forward to January of second semester. I've changed a lot because my first semester of uni has ended and I've joined Greek life. We meet up for the first time since to talk, and we talk and we talk, and we get back together (Pro tip, bad idea). We date once again for 5 months. This time, things start out well, but sadly the same things start up once again. We're fighting constantly (at least 3 times a week), she's paranoid and I'm not helping because I get frustrated and also say things that aren't so nice or are hurtful during fights. Then it's cinco de mayo (May 5th, yes just in case you really don't know) and also conveniently close after my birthday. Here is where things get bad. On my birthday, there was a huge fight that ended with me walking out of her room with her crying, and me sitting on a park bench alone for hours on the verge of tears. I was extremely upset, angry and didn't know what to do except I needed to break up with her soon. Since we were in the process of moving out of the dorms I decided to wait 3 days to do it. Now it's cinco and I'm at this party, and the unthinkable happens. She calls me, and we get in a fight that I'm at the party. She's mad I'm out at a party and I just lose it and say "we'll talk about this another time" and leave. I'm there with all my friends, trying to say goodbye and want to enjoy my last night at school. I then see this girl I knew from class at the party and we dance. Then the party ends and I walk her back and I go home. Now, I know to some that this may not be a problem, but to me it was. I realized that me dancing with that other girl would break my girlfriends heart and she would count it completely as if I was cheating on her. So she calls the next day and I don't want to tell her about it and end up breaking up with her on the phone because of all the previous reasons (also don't do that if you can't help it, it's a horrible idea). So fast forward 2 weeks and we're sitting in my living room talking and I tell her everything. I tell her about the party and the dancing and just like I thought, it breaks her heart and she's bawling her eyes out. At this point I feel terrible and hate myself for it, and out of no where she wants to get back together again. Eventually I say yes, and it lasts all of 1 week, then ends in a rage breakup outside again. After this, we see each other twice over the next year. The first time is an awkward 4 day encounter where we try to act semi friendly / back together and ultimately end it, and the second time is what I describe as the worst day of my life where she berated me and broke me down mentally and emotionally. I've spent more time trying to apologize to her for what I did than I could ever remember and I know I am partially to blame for why things went wrong, but the problem is that in her eyes, we were a perfect couple until I started fucking everything up.

Moral of the story: getting back together with someone you believed it wouldn't work out with will only cause both of you pain and resentment. You'll make them hate you because you're making something that was "perfect" not work over and over again and you'll begin to resent them for the constant feeling of disappointment and failure that comes from a bad relationship. It's a lose lose situation. It is hard because at times there are years of emotion and investment tied into a relationship, but by not being honest with yourself, you'll only end up hurting the other person more and more.

Tl;dr don't do it.

Apologies for mistakes, cell phone life.