Firstly, mrsnlw, like all the most recent posters I commend you for your courage in coming back. It must've been hard, because pretty-much apart from Clumsy, everyone was in agreement against you.
And here are some
from me for you too. And, as others have said, do please get medical help and support for yourself.
And I also commend MN posters to changing their tone when OP came back too. Reading these 9 pages, I've been aghast, amused, entertained and finally humbled.
When my dd went to nursery I was very anxious too. And nursery definitely indulged me in that, because they recognized how anxious I was. I did learn to trust them and step back eventually.
But what you say about thinking about him every second when he's not with you - yes, I recognize that. I was like that too. And if she'd had a bad morning or cried when I left, I was buggered for the whole day until I picked her up again. I do think that's REALLY common, though.
As your DS gets older, though, you will be expected to step back more and more (esp when he goes to school, esp if that's a state school). So I would advise you to try and practice doing that sooner rather than later, or it's going to be a massive shock for you.
I don't mean this to sound harsh, especially if you're low. So sorry if this is inappropriate for someone with depression and/or PND - if that is what you have. But I think part of parenting is to recognise what is 'our' stuff and what is 'theirs' and to react accordingly. I.E. is your DS showing anxiety with his change of KW? Is he more cry-y? Disturbed sleep? More cling-y? If he's still reacting normally, you might consider it being your issue/worry/concern and chill a little bit. I think this comes up for parents all the time. We feel "slights" at our DC which they don't even notice. Or we make or refuse social plans for them based on our agendas or needs. For me, part of being a better parent is learning to recognize what is important to my DD and what's only important to me.
I wish you all the best, and I really, really admire you for coming back after pages and pages and pages of posts to fight your corner.