I don't have any words of wisdom I'm afraid but I just wanted to share that reading your post completely reflects how I am feeling at the moment and also feeling very isolated because my family also do not understand why I am so sad about someone who has treated me poorly. Like you I am thinking about how it was only bad towards the end, he was never verbally or physically abusive. We shared so much together, our families, home, hobbies. I was with my partner for over 5 years and he has been part of my entire early adult life (I'm 26).
I'm dreading Christmas and I am usually annoying everyone making plans and getting excited in about October!
It is hard because for most of our relationship we were happy and his alcoholism developed alongside us and for the most part I don't think he even knew what was happening. The horrible thing about this disease is you often only find out when things are already too bad. He has become someone I don't even recognize- sure it would be easier if he had abused me but do I want to stick around until things get worse until I have the strength to move on. I have been told by others here it will only get worse.
I also struggled with him letting me go so easily without a care. I think about our lives together everyday and miss him so much. I have to believe everyone says it gets easier for a reason and just take one day at a time. We cannot numb our pain with drugs but we are healthier for it. That is no way to live and to be honest I don't want to go on as if it never happened-even if he does. It meant a lot to me.