You're not doing anything wrong, at all.
He's not seeing (or deliberately ignoring, maybe out of guilt) the enormous impact that his illness had on you, too. I've been on both sides of this and actually, found supporting someone very mentally unwell harder - at least when I was very mentally ill I was more selfish and self-protective, but when I was supporting DH I was exhausted and having to do so much to keep him afloat too.
Also, a caregiving relationship is not good for attraction and connection - it takes you from equals to unbalanced in some way, and it can be hard to work your way back from. Ditto for being very financially imbalanced - it's tiring and a lot of pressure and resentment (not necessarily by choice, but it can feel that way).
And, in this case especially, the fear that you 'let' yourself get comfortable with the status quo again and it suddenly goes difficult again - it's a huge shift in your relationship you've been through, it's no wonder you're feeling the after effects too.
He needs to understand you went from 'wife and equal' to 'emotional support, sole/main financial provider, sole/main childcare provider, without the same support or connection from your husband'. You don't blame him for that, but that it is what happened, and it isn't something you're going to snap back and be fine from overnight.
I suspect some of it is guilt - like acknowledging the toll on you will make him feel bad for how his illness affected you, which isn't his fault but is understandable. But it's still not fair for him to expect you to just snap back into perfect-marriage mode considering the long shadow mental illness casts over a relationship.
It's good that you're in therapy, but some suggestions...
- Therapy together (if it's possible)
- Talk about what specifically he's missing: it may just be that you've not elaborated in your OP but if he's just unhappy with the general 'feel' of your relationship, it'd be useful to know what it is exactly he wants to fix (so you know how to, or if you can, fix it). Is it sex? Quality time together? Do you no longer discuss things with him jointly? Does he feel like you get on with life without him? Have you stopped being playful and fun together? Does your relationship feel more functional or transactional?
- Think hard about what you need from him - you've spent 2 years giving a lot. What can he do to make you feel looked after, loved, not like the caregiver? Can he change things to help that? Can you give him (back?) a bigger share of responsibilities on certain things, or can he go back to buying flowers and your favourite takeaway every Friday like he used to (or whatever!).
- Do you still love him? As in, in love with him? If your immediate, guilty thought was no - is it because of something he is or isn't doing? Is it 'yes, but...'? What I mean by this is - it seems coincidental that you'd just fall out of love at the same time he was ill, so although you can leave a relationship for any reason you want at all, it seems to me it's not him you're not in love with, but the situation you've been in. That's fixable, over time, if you want it to be (and if he's willing to do the work too). On the other hand, you deserve to be happy and if your feelings about him have fundamentally shifted, that is okay - you aren't required to stay with someone forever just because they were ill. It would be hard and you'd feel guilty, but if you genuinely don't think there's something worth working on here, don't waste your life being unhappy with someone you can no longer love how you want to.