Oakleaf, I would have to be on LPH's side. I know it's not the common opinion, but I really believe your marriage *comes first.* Before parents, before kids, before anything else, in terms of relationships. An elderly parent should not be the breaking point for your marriage. You have the right idea in sitting down and discussing the boundaries with your DH. I would suggest also, getting some outside feedback. I don't know if you have siblings, but having a discussion with a social worker/counselor/therapist who deals in elder issues would be warranted. Your DH should be included and vice-versa. Sometimes, we are not aware of services that are available. I am going through this with my dad now. He is fairly healthy, but there are other issues. My brother lives in the same city as him and has always been the caretaker, but he is sick of it. I hooked him up with the Jewish Family Services Elder Resources program, which is quite comprehensive. I am sure other family service agencies have similar programs. My DH had an emergency type of situation, where both of his parents became incapacitated and had to be hospitalized and moved into assisted care within a 3 day window. He flew to Phx and the 4 siblings found a social worker who dealt with just these issues. They had the apartment cleaned out, stuff put in storage, and the parents' medical situation under control in 3 days.
I feel for you, but I would not even consider harming my marriage for a parent. You can help, but you should not stop your life.