Hello and welcome to the Forums JJJFL.
I was drawn to your post because I too am a carer for my husband. Although not specifically for his MH, it is more for his physical health. It's me who has the MH issues. I used to work full time, but felt I needed to reduce my work hours early last year in order to better care for my husband needss. He is suffering from a terminal illness. So although our specific circumstances are different, the emotions, feelings of helplessness, and our desire to do what's best for our partner is very much the same.
Its a very difficult thing to weigh up how much your partner needs you to be there as his main support, as opposed to how much you feel you can give. There is only so much you can do after all. And if you are doing yourself harm by making changes to your own work and personal time, to help him, then you are not doing either of you any good in the long run.
Can I suggest that you ensure he has adequate professional support as and when he needs it. And also that he knows you are available if he needs you any time. Make sure he knows he only has to ask. If there is a stretch of time you feel he would benefit by you being around a bit more, perhaps you can take some personal leave from work to accommodate those needs as they occur.
He probably needs to know he is still an independant person, and not reliant on you all the time. So give him some space by continuing work, and not allowing him to feel he may be a burden on you. Its important that you continue to do things for yourself as well. And that includes your work, getting out with friends occasionally, continuing with any sports or hobbies that you enjoy etc.
I hope some of this may be helpful for you. Wishing you the best.