1. Do your best to do only those things that you can do willingly, and for only as long as you feel mostly good doing them. Setting a time limit can be really helpful.
2. Focus on those things about your friend that bring you joy or laughter - be they memories or conversations / activities you can enjoy together now.
3. Recognize that you are stepping into your friend's life, not creating it; and that if this becomes too much, you can / must step back out. This is where an important choice exists, and seeing it as a choice often helps.
4. Also do some things that really take care of YOU.
5. In any case, find or create humor and perspective where you can, and this will help.

Recognize that you have the ability to set limits or boundaries. You're dealing with the life of another, so take a step back to allow for a more normal, less dependent life. Even in the most dire situations, you must care for yourself, and not become the sole source of help for long periods of time. No one alone can hold up a safety net for another! It takes a Personal Safety Net team!