First of all I'd like to say its a well written piece, and could be a great pop song.
Now you've requested constructive critique.

Work on the arranging and mixing.

Mixing: I would make the bass tone more defined and punchie maybe a nice loud round sounding Jazz tone worked it in with the drums which could be a bit snappier and crisp, giving the piece a clearer oveerall sound.
The horn sounds arent too bad but could be a bit more in the front.
I would also thin the vocals and reduce some delays.
Arranging: It Begining around 3:10 starts to get a little stretchy around 3:00 I think if it were cut right to the section at 430 and then end would make more enjoyable.
The 2nd part at 520 apx "dont really know you" musically for me doesnt work with in the context of the song. I think if the lyric were interplolated with the earlier section at 420 it would make a good ending.
Id keep it all at around 3:30 long.
Hope that helps...JMHO