Jealousy with a large helping of guilt

My mother-in-law(MIL) is going on stroke 3 and has been incapacitated for over a year now. We were very close and I'd like to think that somehow we still are. What has been bothering me for a few months now is some jealousy I feel because my spouse dedicates about 95% of her time to care for her mother. First off, culturally speaking a nursing home was and mostly still is out of the question. Neither of us want to do that. I myself can not contribute like I want to because I've taken a postdoc which has pulled me from my home for the time being. My spouse and MIL can't be moved to my location an they shouldn't be because my postdoctoral appointment is a temporary one. This means I get far less time with my spouse that I think is healthy. Hence, when we are together I want to monopolize her time with me, and my MIL, who is still lucid also gets jealous of me. This is proving to be a real problem which reared its head this Christmas vacation. I see all of my in-laws basically ignoring their mother outright, and my spouse shouldering the burden of care and patient advocate almost completely alone. This causes me to experience a huge array of feeling from resentment, jealousy, and despair. Sometimes the feeling are a bit dark and I wonder where they come from. My and my MIL we very close and liked to spend time together, so the darker feelings are scary for me. My wish is everything will get better for my MIL but, the rational scientist in me knows this will never happen. How does one cope with guilt of not supporting your spouse more in their time of need due to career commitments and how do you not let negative feelings spoil your relationship with your incapacitated family member. Especially when their life is so heavily dependent on your spouse for survival.