New here. Need some advice please

My (42F) boyfriend (43) and I broke up recently. Our relationship was so awesome at the beginning and then everything just seemed to come crashing down after we moved in together. I broke up with him after 3 months of living together. The breakup lasted 4 months. In July we got back together then I ended it about a week ago. I've been trying to make sense of what happened. Then it clicked for me. He told me once in passing that as a child a doctor told his mom he has ADHD. She ignored it. She was very neglectful and abusive as a parent. I've done some research and he checks an alarming number of boxes as far as characteristics of a person with ADHD. The hyper-focused courtship at the beginning then the abrupt loss of interest. Now the hyper-focus is on his "hobby" (obsession). Overspending on said obsession at the expense of necessary financial obligations. Has things related to obsession laying around all over his apartment all the time. The forgetfulness. Has trouble paying attention when I'm talking and always wants to be the one talking. Always wants to talk about his obsession. If we would watch anything other than an action movie he would get bored and zone out. Interrupts me very frequently. Will avoid serious conversations. Has a serious problem with dealing with conflict (also views productively dealing with problems as conflict). Has pretty severe anxiety disorder. Has a tendency to break promises when we make plans for something I want to do, especially if it interferes with his obsession. His obsession, by the way is airsofting. This is basically paintball but with BBs. Essentially he likes to go out and shoot a bunch if people with toy guns. Also seems to fit in with ADHD (needing a high level of stimulation). I still have hope for this relationship. I'm not ready to completely give up on it just yet. We have other complications (his family) but I feel like we need to address one issue at a time. I believe lack of treatment for the condition has caused most of our problems. He and I are currently not speaking. My thought now is that he doesn't realize the damage the condition had on our relationship. I thought that if I mail him some info that might be an eye opener for him and he'll get help for it. What are your thoughts on this? Does anyone else have any additional ideas on what I can do? I'm also planning on writing him a letter about this. I could use some advice on what to say in it. Also, has anyone else been in a similar situation and made it work?