My husband has a long term affair - the OW is pushing for divorce, he resists and tells her he needs more time. To me he says that no matter what he will never leave me and he wants us to live together forever
Hang on a sec... to which one of you is he telling the truth?
It may very well be that both of you have a pull on him. She has an emotional tug which has him "totally wrapped around her, obsessed even" (and which, because it's emotional, could ultimately win out), and with you, he has a vision of 'living together forever'. Neither of these scenarios deal with reality on his part.
That suggests he has a conflict about letting go (of either one of you). This status quo can go on for some time! Either you have to excel at meeting his emotional needs far better than the OW, or you need to drop the rope and let him experience whatever it is he's looking for outside the marriage, hopefully that he'll find it was an illusion.
The problem is that quite often I just cannot hold my tears... sometimes I am just not able to hold on and start to cry in the middle of the sentence. Do you have any suggestions how to get better control?
Outside of actively avoiding thoughts that you already know will bring on tears, there's not too much you can do. Sometimes, you can acknowledge to yourself that you feel down, that it's OK to feel that way, and tell yourself you'll deal with those feelings later. They have to be dealt with. Some people find it worthwhile to take a little alone time to vent, perhaps writing out everything they're feeling (never showing it to their mate). Others find that when these thoughts come, they substitute another action; they go for a walk, for example.