I believe when it comes to differentiation the person you need to trust is yourself.
This is exactly what traumatized people do. They trust only themselves and no one else. However they can still be extremely enmeshed, so differentiation and trust in others are two different things.
The way you come to trust yourself is by taking care of yourself.
Yes, this is what they do. But it still does not allow connection because the walls built up by the trauma block many vulnerabilities that might come about through connection. Taking care of oneself does not mean connection.
Because of my FOO issues, I need to concentrate on mothering myself in order to maintain differentiation. So now instead of a make-believe lover, Hank, I have a make-believe mother, Gloria. Pretty much she is a cross between Goldie Hawn and Cokie Roberts. My life will be great if I follow her advice.
The difference as I see what you describe is that you still WANT connection and therefore are still willing to place your trust in someone else. You are still willing to take the chance of being hurt. What do you do for those people who decide they will not take on that chance any more?