Need help on moving on

Hi! So first of all, I would like to say i'm not used to share my feelings with random people and that makes this harder to explain which might lead to this being a huge wall of text so, apologies in advance. My ex and I were together for almost 2 years, which seemed like a lifetime back then. She broke up with me because she was going to another city to study and she felt like she would feel "trapped" if we were still dating when she went there. This happened literally out of nowhere, we were completelly fine one day and the next she just decides to break up. At that time i also had some other bad things happen, which all led to depression and isolation which then led to building up severe social anxiety and then into therapy. It has now been 3 years and i cannot let her go. I still think about her every single day, as she was (and I still consider her to be) the most important part of my life. But i've come to a point where i know i have to let her go because it's ruinning too much of my life and i really need help with that. Thank you in advance.