Boon, I haven't got any words of wisdom but you could've been writing my thoughts. My relationship was very similar to how yours sounded, my partner too was very considerate of me most of the time. It was mainly my issue with his drinking, the not knowing if this night would be the night he had too much and would be argumentative, that caused a lot of the tension. I was permanently on edge around him drinkng because of incidents that had happened sporadically. However, I do see now that he was never going to stop drinking and I was never going to stop having an issue with it so it was never going to work. Admittedly I shouldn't have taken 13 years to come to that conclusion!
I'm not 100% sure if my ex is seeing someone else or not, I have suspicions but no proof and I'm trying not to dwell on that too much. I'm looking at the relationship with a slightly clearer mind and I know it wasn't good to live in a constant state of "walking on eggshells" and conflict.
I am terrified of life on my own, I'm not going to lie but I think I also realise that I cannot go back to the relationship. It was unhealthy for both of us.