I can remember what the beginning of going through this feels like, so let me offer you some of the advice that I got.
First, he won't forget about you. The best thing you can do right now is honor his request. Now, I am not telling you to cut all contact. But at the same time, you have to learn to have enough respect for self to set some boundaries.
First of all, no one deserves to be yelled at the way he is yelling at you, regardless of any kind of mental disability. However, there is a way to handle this with style and grace. Let him contact you, however, if he begins to yell, then calmly tell him that you will not speak with him unless he is willing to speak and not yell. Then hang up the phone.
Second, when he does call, do not talk about he relationship. Right now, this is the way he feels, and you need to acknowledge that. To tell him that you know he loves you comes off to him as "I know what you feel, you don't know what you feel, therefor it doesn't matter how you feel." Now we both know that is not the case, but he will use that. Right now, he is using anything he can to justify his actions. Therefore, don't give him any reasons. Be pleasant. Be kind. Tell him you understand, even if you don't. "I understand" is a great line. You are not agreeing, but you are not disagreeing either.
When you get sad, mad, homicidal come here and vent. There are great folks here who have been where you are.
But the biggest thing, listen to what he says. Then, ask yourself if there is any way you can improve upon his complaints. Don't ask him, ask yourself. DBing is about working on yourself, because none of us are perfect, and we can all improve.
Remember, finally that there are no guarantees. Some reconcile and some don't. But if you follow the steps, and do the work, you will end up better for it in the long run.
Im still standin better than I ever did looking like a true survivor feeling like a little kid Im still standin after all this time and Im picking up the pieces of my life without you on my mind..