Oh dear, bluebird. My experience isn't good, but my ex had a midlife crisis and an affair. I'm not sure how much of our relationship breakdown was related to my DS's SN and how much would have happened anyway. We had definitely stopped communicating about anything except the kids and day to day stuff. I don't miss him, per se, just someone to share the load with. And his money! 
If you want to improve things, if it can be saved, it's clichéd, but you need to make some time for each other that's not to do with the kids. Some many men need their egos boosted. No sex for months is not a good thing. Maybe post on the relationships board as well? I found it invaluable. Some posters there will assume he's having an affair, because that was their experience, but there are a lot of wise women on that board.
When it got to the stage that I realised something was wrong, when he was being constantly critical and impatient with me, when sex had stopped, when I felt uncomfortable undressing in front of him, my ex had already started his affair, so for me, I'd already left it too late to change things. I hope you have still got something worth fighting for.
Oh, just reread that you don't want to post on relationships. I namechanged for that board. I was very, very honest, quite self-critical and got some great advice and some more 'challenging' answers, but they really are the experts.
If you have come to the end of the line, or still have something to save, counselling may be useful. Preferably together or individually, it may help you to work out what you want to do, either way. 
((((hugs))))