Unfortunately as yet it sounds as if Dennis has failed to bond with you.As Judy correctly said he has picked up on the fact that you show fear of him biting,you need to learn to be a little more confident with him, if you show confidence he may begin to pick up on that & grow in confidence himself.As for letting him out of the cage just leave the door open,a big tip for getting him to return is make his cage his only feeding place, he will soon return when hunger strikes.
As for clipping as the others have said,it is a personal decision,if he is crashing into things he risks injuring himself,perhaps discuss this with your avian vet.