ignore it pretend like it doesn't exist because the only problems we really have exist only when we acknowledge them? Try to avoid that person as much as possible?
If that person loved me, I would show them how it hurts by doing what they do. Sometimes, if you take a different view at a situation what you were blind to see becomes clear. If this approach doesn't work, and you truly loved that person don't give up on them. You don't need to be around them all the time, but make sure you are there when they need you, and they WILL eventually need you.
That's a slippery slop. A lot of the time a self destructive person inst ready to face there faults and it may be hard for them to understand how they are self destructive. I'd try to little by little show them how they are a wrong in a given situation. I feel like if I laid the whole truth on them at once they would reject my opinions. No one likes to here how they suck especially a self destructive person.