I don't think there's any particular way a session "has" to end; I think it's between the pair, you two. Sounds like you got comfortable with a certain routine/pattern you saw the two of you doing instead of just your response alone. So, when he didn't do his "half" in your mind, you didn't know what to do :-)

I'd start the next session with relating what happened to you so he knows you like the routine and that can be shared between you? Obviously he didn't know what was going on :-) so I'd share your "half" and help make it a whole/shared moment.