<human>: Reddit, I am need of some serious help here. Using a throw away for obvious reasons. I (31M) am entirely having a break down when it comes to romantic relations. 

Back story here, I dated a girl (now 29) many years ago, eight to be exact. We dated for about a year. I loved her, and at the time she was the one I thought I would marry. We had a terrible break up due to her infidelity and the fact that we were both in the party scene and just all around bad people.

 About 6 months ago my ex from years ago came back into my life. She sent me a text basically to start a conversation so she could apologize for everything she did years ago. We talked a lot of things out and decided because we were both different people than years ago we could try and be friends. My current SO(29) of two years was supportive, but a bit hesitant. Well she was right to be. Now, six months later I have woke up and realized that I am terribly in love with my ex from years ago. I want to be with her and no one else. Here is the problem.... I still have a significant other, and so does she. The ex actually isnt even interested in seeing me that way again. She is in love with her SO and they have plans to marry.

Summarize the given text in a few sentences.
<bot>: I want my ex, my SO wants me, and my ex wants her SO. How have I allowed it to happen, and how do I undo all of it?