Does he ask your friends about you?
Is he interested in anybody else?
Is he warm and friendly towards you?
Does he seem jealous if you date other guys?
Does he ever reminisce with you about the times you've shared?
Has he returned everything to you from when you were dating? Ie. Gifts, cards etc.
Does he find reasons to talk to you whenever he can?
Has he apologised to you for his part in the break up?
Does he ever ask you about your romantic life?
Does he seem a little awkward when the two of you talk?