Tips on how to handle "processing time."

We have this reoccurring problem in ALL of our arguments.   I say he's just being avoidant, he says he needs time to "process" what I'm saying.   We need to break this cycle and I'm not sure I'm in the wrong, but maybe I am and could use help.

Any time we have an issue, he won't bring it up.  In the early days of my relationship, when I would bring it up, he'd accuse me of starting an argument at an inappropriate time.  Which, of course, would start an argument. 

But now, if I bring up something, he immediately begins cleaning the kitchen or doing some other chore he doesn't often do.   When I press him to talk about whatever, he says he needs "time to process."  He won't give me how long he needs to process, and if his processing time runs too long (as it often does), he will need to go to bed and I'm being unreasonable by wanting him to stay up and argue. 

We have been together since the 90s.  I do not know how long it takes him to process whatever, because once the immediate situation is over, if I attempt to go back to the discussion he tells me that I'm "bringing up the past," and that he "doesn't have my memory" and can't remember what role I played in whatever bad situation we were in and it's unfair because I remember everything he did.  This goes for EVERY tough conversation.  And by tough situation, I mean things as benign as "what are your work hours?"  (literally, me finding out that his hours are 7 to 3:30 took three actual arguments) as well as harder conversations like "I think we should have a trial separation." 

And watching someone go blank or leave the room when I'm trying to have a serious conversation is INFURIATING.  So I always end up yelling.  I think he's just playing possum to avoid a hard thing.  He says I'm not giving him long enough to process, and that he knows I'm going to be mad, so he's trying to be careful with his words.  I don't know what words he is being careful with, though, because I never hear them.