thank you all so much for your comments - very helpful indeed. I will try to respond to as many as I can (am on a time pressure...)
anyfucker - no, he doesn't make me feel inarticulate, I do that all on my own! He just doesn't like arguments (childhood full of them, the irony being that his - arguing - parents are still together...) and often when I try to talk about things he just clams up. Totally. Doesn't say a word - very difficult to conduct a one-way discussion. It is one of the things that we have talked about since his bombshell and he is trying. I find it hard to pick the right time to bring something up and I think I am probably a bit passive-aggressive; one of my least attractive character traits. I am much better at writing things down, and have started a letter - discussing it on here really helps too.
ziptoes - thank you for the book recommendation, I'll have a look.
mrswhiskerson - lovely post, thank you. He does tell me a lot that he finds me attractive (apparently I have a great bottom, if that's not TMI...
) and last night he said I was beautiful. And there was no sexual pressure behind it.
Talking of sexual pressure, as this (naturally) has come up a lot. I never withdrew completely - we had loads of kisses and cuddles, and often more (yes, I will admit that full sex was not as common as it was, but there were reasons for that). Not as much as he would have liked, but he has a very high libido, and there was certainly never nothing. I think a lot of the issue was the expectation that kisses/cuddles may lead somewhere else, so when I (fairly often) said that I didn't want that he felt that I was rejecting him. Since this all came out, I have made that point and the pressure has certainly eased making being physical much easier - so that has picked up a bit, oddly enough. There is still an aspect of emotional barriers if we go too far though, on both sides.
morebeta - no flaming from me, thank you for your input. It has not been three solid years with no physical side (and see above, it was low rather than nil), as once bf reduced quite a lot with dd my hormones realigned and I felt sexy again - but it was only 2 months before we conceived ds and then morning sickness struck.... tricky to feel sexy if you want to vomit a lot of the time! 
. I'm really not pushing him away, the difficulty is that he felt that I was - he admits that that was a misunderstanding.... But yes, I do see how the physical side of things could easily contribute, and take some responsibility for that. The problem is, what can we do about it? I have been trying (and succeeding) to be more physically intimate - but don't think he would want me to have sex with him if I was not happy with it. From a man's pov, if you are doing almost everything but, and getting physical release, is this an acceptable holding pattern for a while? I also don't feel that our children are totally taking over - I have tried to balance everyone (not very well, clearly....
) but it is natural that the balance shifts, trying to find a new dynamic that suits everyone is the key. Still working on that one....
ITNG - sorry, but you are wrong in that final sentence. I really do want genuine male opinions, and will even allow that a lot of what you have said may be right . I really appreciate you gents who have taken the time to reply, I just want to understand what is going on in his head, and you are helping with that. Thank you.
pickgo - you speak a lot of sense. I think that he told me out of a sense of wanting to be honest, and hopefully to sort things out, although that is one bit that I am not sure about because I think that he does not believe that they can be sorted out. I am trying to understand why he feels like this in the first place, why he didn't tell me earlier, why he is feeling so pessimistic about sorting things out and what we can do about it.
Sorry this is a bit long, and thank you once again for all comments.