The best thing is to be there for him, but not to demand that he watch out for himself. At least this is true with me. I knew I was not well and I knew that I did not want to hurt myself further, but having people who were worried or telling me what to do and how to do it only made me rebel.
I know that that was the wrong reaction, but I am still doing it. If someone says "Oh, you really should take it easy." Well, I just want to prove them wrong, and then I will go back to my room and sleep for three days where no one can see me. The best friend I had was someone who would say, "Hey, I was thinking of doing this, if you would like to come that would be great, or if you would rather do something else." Then I could just say, no I'm not feeling up to that or yeah, why not.
As far as the memory thing goes, making a joke of it was the way my friends and I handled it. They would pretend that I had said something or done something horrible and then I would really say something to knock them off their rockers.
People who are going through this feel isolated and weird, it is really nice to be around people who make you feel normal and OK while not explaining away or discounting what is going on.

Good Luck!