Maybe your DH is depressed himself Suffolk? It's not unheard of.
You'll be better off without him I'd say. Three bouts of depression sounds like a lot. I wonder will you feel a lot better without him?
Can you go to your GP and get tested for mineral and vitamin deficiency. Also for hormone levels. It might be that you need HRT or thyroid medication rather than ads?
I think you're in shock for now, is there any way you can be signed off work? Also I agree it sounds like he's made plans to be somewhere else, so I'd accecpt that and get in contact with a solicitor.
I'm sorry this is happening to you right now, and wish you and your dd all the best.
Id wish your DH all the best, but I think he knows how to look after number one, without my good wishes.
I do think he could have kept a lid on it for another few weeks, and also to have offered more of an explaintion for your mental health and closure than that old chestnut "I don't love you anymore".
Maybe he'd agree to a mediated separation, it would give you an opportunity to off load how you feel, hear his side, and let him know his cruelty is unacceptable. The mediator will insist on kindness and respect.
I'm my experiences, life is never how we think it will be anyhow- relying on a certain outcome brings unhappiness. Being open to life's changes and opportunities is a happier way of looking at things. Nothing in life is predictable actually.
Good luck.