Hi @Primrosehill82 i have to say I do have experience of this as i'm living through it at the moment. I'm not married but had a very happy relationship for nearly 5 years before suffering a mental health breakdown (after some trauma & other stressors) A few weeks in to my illness I suddenly felt like everything was wrong with my relationship. I felt like i'd never been happy with my partner & everything was a lie (even though i know i was blissfully happy before) we never argued & were on track for a happy life together. I now can't get past these thoughts, and like your husband, I feel no pleasure in anything & feel completely hopeless about the future. I have confided in my partner now (as for a while I was hiding this from him) and he's understandably very sad but we both believe it's the depression and hope things will change. I think the problem is that in my mind "i will only be happy if i'm not with him" and therefore anything else feels unbearable. My mind is making me see that as the only way out so I imagine this is what your husband felt. But I would say it has to be the depression causing this. Because it literally takes ALL feeling away, like you could happily not see that other person again, and when you KNOW you loved them madly before it's crazy to think that you wouldn't at least have some feeling towards them. It's honestly like a switch and you start to go as far as resenting your loved one.
This must be so awful & painful for you though, but you have to know it's not your fault! My partner is absolutely amazing & has proven to be even more perfect in the way he has handled my illness so patiently, and yet I still can't change my mindset.
Your husband will no doubt be feeling a lot of guilt but his mind will be telling him he's done the right thing.
I'm still fighting for help and (despite trying a few) still feel like there is a medication out there that might change my thoughts. So encourage your husband to speak to healthcare professionals for a medication review. (and if he's not on any - encourage him to be!)
Again this must be so painful for you, but remember he's not well and at the moment the commitment to you and the family is a no go for him. So, if you do want to spend time with him - try to keep it to the present moment & more as friends/light hearted, rather than focusing on him leaving. Hopefully more time like that with you, will trigger some of the old feelings again. If he thinks spending time together will give you false hope, he'll just avoid it.
I would give anything in the world to just 'click' back to my old feelings but i'm trying to remember i'm unwell and as my healthcare professionals keep telling me - don't make any rash decisions during this time. But that doesn't make it any easier for me or my partner.
Sorry for the essay here but one other thing I've been told, is that when you're severely depressed, your mind/body tries to make sense of what's causing it, and therefore will pin it on to something in your life. And what can be bigger than your relationship &, in your case, children. So that's the brain saying 'this is the problem, get away from it'. Sadly, if my partner turned around to me at the moment & said he'd had enough, it would give me relief because I wouldn't be the one hurting him.
Again remind him he's unwell and encourage him to access counselling, medication support, relate support. And take care of yourself, don't be overthinking if it's something you've done or could have done differently, believe me, it's the illness! But you also have to prepare yourself for the potential that his mind will never switch back, and in that case you can be there as a support for him but need to think about driving your own life forward. Mental health is worse to me than any physical illness because it can cause this type of devastation and even worse, you can't communicate about it. But it can make people very selfish also, it's self preservation (quite literally, as the thought of staying in my relationship makes me feel suicidal, and your husband might have been the same). So you might have to start being a little bit more selfish yourself & thinking about what your limits are. I'm sending you love and I guess an apology to you and my partner, and anyone who finds themselves on the wrong side of this awful illness. xx