I'm expecting my friend to say goodbye to me when I leave.
That's quite a normal thing to want.
I know that I will leave his place soon and I bet he will say "goodbye" to me.
That's a reasonable assumption to make, if you are planning on leaving soon. When people leave, it is expected that you say goodbye, especially to your friends.
I think it may be a logical fallacy. I am only saying goodbye because I want him to.
No matter what the reason is, it's nice to hear goodbyes from people you know.