He'll tell you.
He wants to move upstairs.
He might stare at you alot, asks his friends about you
He probably only wants you for your vagina.
Because she wants to live with her boyfriend.
It sounds like there are no signs.
she flitrts with you while they go out
I think you should not move in with him intill you are married
He usually likes to be around alot of girls. And he wants to do stuff to make him seem better.
Some of the signs would be when she flirts with you,when she does you favors,or when she invites you to a movie,Those can be some signs,although they might sound gay!
Let him kiss you. Unless of course you don't want to. If you don't inform him or, send him signs you don't. If you do, show signs you do and don't get nervous. (:
From my opinion, he will always stare at you until you walk over, and then the move happens.