OMG -- That would drive me absolutely NUTTY!

Since you've told him about this, why does he keep on doing it? Doesn't he realize he's talking all the time? Is it just something he does without realizing it? Can you come up with a "code word" to say when he starts doing it, to let him know that he's doing it again, and he's to SHUT UP when you say that "code word?" At least then you wouldn't have to bite his head off. LOL
There's got to be a "condition" or something that makes him do this. Perhaps he needs to see a therapist. Have you considered asking him to see someone? This just doesn't sound normal to me. It sounds anxiety ridden to me. Is he an anxious-type man? Is he always worried, nervous, edgy, testy, etc.?
Dearheart, you do NOT sound stupid by any means. How you have endured this for "many years" is beyond me! I probably would have killed him by now, or else put a hit out on him.

Having to live with someone who does this is just too cruel. lol I would ask him to see his doc first. Perhaps there's some medical reason. THEN I'd get him to a therapist if the doc says he's ok.
I wish you the very best my friend. Please let us know what happens, will you? I don't want to have to think that you're living like this forever. So PLEASE let us know, I beg you! God bless & take care. Hugs, Lee