Find another friend.
Really, they come and go though ones life.
Well, first and foremost I would make sure they were getting the medical care that they needed. There is medication that can help with the symptoms and therapy.
There are support groups out there for family/friends of people with schizo. It's a hard thing to deal with with and having someone who understands can help a lot. Search the internet, I'm sure you can even find support groups online. Hope this helps...