Faye,

Just sharing observations, no advice…

What strikes me about your post is that both of you are insecure with yourselves and therefore with your relationship.  That he is not transparent and honest with you, e.g. his “teasing”.  That seems like there will be always this doubt for him and for you.  He does not want to totally let go of this girl.  He is insecure about your ex.

You are both stressed and in your mid-20s.  You two both are going through this growth period in your lives as far as maturity, career, and relationships are concerned.

Mark