He's doing it because he wants any reason to justify his actions.

Well then you could put it that way.
"Hey, will you give me notice if you intend to move out. I'd like to have some lead time so I can get a roomie to help with expenses." but what would it profit you?

Why are you letting it consume your life?
It's not in your control what he does and does not do.
So let's say you come home and he and his stuff is gone. You're half expecting it.
Will you let it devastate you, or will you say to yourself, "Ah, I thought that's what was going on." and then be relieved you don't have to wonder anymore?

What would you do if it WAS just a roomie?

Perhaps take that attitude.

BITS
Me-51, WAS-52
Kids 2
M-26yrs, H.left 2009, 2 more Bomb drops, Reconnection spring 2013
Change is inevitable, personal growth is a choice.
Love is a action and choice you make, every day.