Other People Are Reading
Stay in regular and consistent contact. It can be hard to watch a person die, but it is even more painful to know you let them die alone.
Allow them to lead the conversation and listen to them, even if it means you both are silent. If they want to talk about death, let them. If they don't and want to focus on happier things, give that to them.
Don't try to tell them how to feel or assume you know how they feel. If they are having a down day and are gloomy, let them be gloomy. Trying to create false cheer isn't going to change how they feel--it will only make them feel like their feelings have no value or that they are misunderstood.
Deal with your feelings on your own time and don't foist your sadness, guilt or anger onto them. They are dealing with their own emotions right now and do not have the time or strength to deal with yours too.
Be there to help and comfort them--not the other way around.
Offer your help without fanfare. Many people have a hard time asking for help, even when they are desperately in need of it. Ask if you can pick something up for them while you're at the store, or see if there is a load of laundry that needs to be put in the washer. Don't just tidy up around them or bring things to them; it may make them feel like you consider them to be helpless.
Support them in what they wish to do. If they want to work, take classes, try something new or whatever it is, encourage them to do what makes them feel vital and alive.
Be yourself. This is the most difficult thing to do but the most important. Right now, with all that is changing, some things need to stay the same. You are a unique part of their life and they need you to stay there because no one else can truly fill your place.