(((HUGS))) Jen!
I can understand a little of what you are going through. I'm having behavioral issues with Rocky who sometimes marks the cat beds/furniture and health/behavior issues with Ripley who likes to pee and sometime poop in the dining room unless I watch closely and let him out in the garage to his "private" litter box . Thank goodness we put down Legato carpet squares in that rooms so I can just pull them up to clean or throw them out and replace if too bad. We got wise and replaced the old carpet with that stuff the last year with senile Disney in the house. It's not beautiful but it's better than the alternative.

I wish I knew some words of wisdom to help but I can tell you that your dark thoughts are normal. I know some people will probably blast me for saying this but there are days I wish Ripley would just make 'that' decision for me. He's 15 1/2 years old, whines and grumps like a true "grumpy old man", has potty issues, has barfing issues with an extremely sensitve stomach, constantly pulls his hair out with his OCD and often is just not pleasant to be around. He never was an affectionate cat and back in the day he was down right mean and often I was terrified of him after an attack - I still have scars. I just never in my wildest dreams thought he would live this long and from the way he acts he's going to out live us all!

Anyway, I just want you to know you I understand and you have my support and my sympathy.