The responsibility falls on both people
The reality is that, sometimes, a spouse needs to suck it up and accept that, temporarily, his partner won’t be able to pay much attention to him. If it truly is only temporary and out of anyone’s hands then, simply being patient and refraining from doing anything dumb (like cheating) will get the pair through it. Meanwhile, if you’re the person who is distracted by caring for a sick family member, make sure to tell your partner that you understand his plight, and you really appreciate how understanding he has been. Just acknowledging the experience of the other goes a long way.