Good question from darknes..really ponder that. Along the way I have stumbled, been angry and felt defeated. Its a tough concept that we only control ourselves.
My MR fell into a routine as well and tough when you dont see that in the moment. My H has moments of caring but lately is cold/distant. I would say let the apathy fuel you in positive way--know easier said then done.
I have struggled to stay busy and refraining from reacting to things. Those stumbles become goals to not repeat. I know you are down, I have been lately as well. Keep posting for support and wish you well.