Twinset - have missed a fair bit as I drove home from work and put the dc's to bed.
I once had someone tell me to stop living in my head so much, and so starting living in my body. I thought it was odd and I couldn't quite connect to it until I really tried it, and I could see what they meant. I suppose, it's why people meditate - to get rid of all that noise in your head.
I really sense that, with everything that has happened to you (I thought there must be some serious trauma lurking) you have both done incredibly well to weather the storm. From everything you say, I can't help but think that this relationship is worth some effort to bring it back on track.
Don't take this the wrong way, as I know I am often guilty of this myself, but is there anyway the whole announcement of maybe leaving your DP has been a bit of an attention seek, or a cry for help? Were you in earnest when you said it, or were you hoping to shock him out of his current ennui/general funk and make him realise that the situation is serious?
If he loves you like you say, no wonder he was so hurt and suggested separate rooms. I would rectify this asap if it's possible.
Can you think back to things you used to do together and try and go back to one of these activities? A shared passion?
Other than that, you may need to try and address your depression if you haven't already. I suffered it and it was the worst strain ever on DH. He was never allowed any problems - mine were always far greater, more dramatic. There were times I couldn't even get off the sofa of a weekend to take the dc's out, even though I work all week FT and hardly see them. It was ghastly. I was surprised DH's patience lasted as long as it did.
Am possibly rambling now, but your post has really touched me, and I just hope somewhere in all these posts you get the insight you're looking for.