How to communicate without upsetting each other?

My boyfriend has been my best friend for 7 years, and we have been dating for over 2 years. We have a lot in common and care about each other deeply. When it comes to communication, not only are we stuck, it devolves into feelings being continually hurt on both sides. We can't seem to break through, and his reactions keep us stuck in the cycle.

He has not been diagnosed with ADD or ADHD, and is still partially in denial that he may have it. I am not a doctor, and I know I am not qualified to diagnose anyone, but everything I have read on this site and others seems to reflect our experience. I have read that it is highly heritable, and his father and brother both have it. My boyfriend is sweet, creative, thoughtful, and funny. He is also very forgetful, loses things constantly, has trouble focusing, gets excited about various projects or goals and doesn't finish them, doesn't plan social interactions, and is habitually late. He has always been this way, and has figured out how to deal with it so he can be successful. He is the "normal" one in his family; energy was always focused on his two brothers with ADD and aspergers. He does not have many close friendships, and keeps everyone at an arm's length so he can generally control the image they have of him. He always says yes to people, and some of his friends only call him when they need something. He knows this, but he says he is okay with it. He is not good at keeping in touch, and does not keep up the reciprocity of friendships. Somehow he has gotten by in life and been successful while trying to manage the day-to-day. He still lives at home because he just graduated law school, and that complicates things a great deal. His family is not welcoming to me, they have many demands of him, and try to tell him he shouldn't be dating in general. 

His behaviors, and his reaction to my unhappiness, make our relationship very difficult. He doesn't understand why these things upset me and complicate my life, because it is how he experiences life and he claims no one else has a problem with them. People have been upset with him before, but no one else in his life is intimately involved with him or trying to have a shared experience. When he is late, he either texts me every two minutes with his whereabouts, or doesn't even let me know he is running late and says I shouldn't care. He often forgets about plans he has made, and sometimes drops doing something with me at the last minute or when we are in the middle of it so he doesn't disappoint someone else. He has a low tolerance for frustration, and can jump into an angry, dramatic spiral if I simply bring up a subject he doesn't want to discuss. He takes everything personally, even if I say it isn't about him. He is easily distracted; we can be in the middle of an online conversation and he will walk away for hours. I always have to plan when we get together because he doesn't plan things with anyone. I have gotten upset because he ignores me (and doesn't seem to realize he is doing so) when we are in social situations where he knows the people and I don't, and then he tells me it's my problem that I felt uncomfortable, and that that makes him uncomfortable. (I am not an awkward person and am polite.) When we are together, I get his attention and consideration in a way that sounds like hyperfocus, and of course it's great at the time, unless I get upset about something. We are so happy when it's smooth sailing when we are together that we even talk about getting married, but I know that we are never able to resolve conflict. He tries to communicate and support me when we are apart, but it is so inconsistent. It is hard to only feel close to him when we are together. 

Whenever the consequences of his actions upset me, he either is completely defensive and invalidating, or gets sad and needs to run away and shut me out. I have tried to temper my frustration and my sadness, but I can't always keep it inside. He takes everything as criticism, and takes no personal or joint responsibility for some of our interactions. I think he feels really defeated by what he feels he can't change. I have brought up the subject of ADD to him, and we talk about it for a little--he says he feels like it would mean something is wrong with him as a person. I told him I understand that, because I have struggled with depression and had to work through those feelings. At the same time, he seems to blame me for our problems. He sees me as the source of his stress. When I asked him why he doesn't forgive me for things, he said that when we first started dating, he didn't remember saying or doing the things I was upset about, so he had to start keeping score so he would have something to say back. This makes me so sad. I have said that I think our real issue isn't forgiveness, but that we hold the other person entirely responsible for our negative feelings, and that we jump to conclusions about motives. We don't entirely trust the other person not to hurt our feelings because of this cycle. We are so sad because we want things to work, but our communication is at a standstill. We can't imagine being with anyone else, so I don't want to give up. And I see the separation between his behaviors and who he is as a person, even if he doesn't. Any advice would be greatly appreciated.