I think it's because the parts of you that don't trust your T are coming from a younger place, and aren't yet fully aware that you are an adult and can take care of yourself. Parts of your brain can still be stuck in a childlike mentality in which your T really is viewed as someone essential to your survival. It's like when you were little, you had experiences of rejection or abandonment or whatever that scared you, and so somewhere in your brain a part of you decided "we should be careful and not trust too much, because we can't survive on our own yet!" Yet even years later as an adult they can still be in there, running on autopilot...