If I remember correctly werent you coming out of a bad relationship not to long ago? ( if not forgive my mind)

As for your current situation.... Your assuming he is going to hurt you so your staying emotionally unavailable.. How to fix it ? If he is someone that you want to see in your life long term, you will need to allow yourself to trust him. Small steps.. Just be good to him and let him know your fear(s) and that you are actively working on yourself..

Take your relationship slowly.

Good luck