Why is my friend disappearing from my Facebook friends list?

[blahblahblah]

The first time it happened last night when I was on Facebook, and I asked him if he deleted his account and he said no, and then it showed up again, and it disappeared again today, all of the comments are gone, and his name from the friends list, but hes still on my chat window.
I know if he was going to delete his account he'd let people know so please avoid the "he deactivated his account" answers. because this is really inconvienent.

[Ren]

It could be a glitch with Facebook. I have issues with my friends list all the time. Send a message to Facebook notifying them of the problem so that they know what is going on and will fix it. I don't know how prompt they will be about it, but it can't hurt.