There are some people who seem to be able to share their deepest self with no particular effort. For them opening up is like simply showing someone the page of the book, and then, when it has been read, showing it to someone else and so on.
I think I've gotten more private as I've gotten older, perhaps because I've discovered that I don't seem to be able to simply "show" people pages. I feel much more like I rip them out and hand them over for good. A piece of myself goes with that person, and sometimes they don't realize it. Letting go of that person, or letting ties drop would be like letting go of myself.
I lose trust in a person when I feel they don't value what I've entrusted to them--why should I hand them out to someone if they aren't important to them? This has happened in many, small reparable ways with people who know me only a little, who only have perhaps a piece of a page. Once I lost trust in someone who had almost an entire chapter. Try as I might, I cannot force myself to trust that person again. I want to. But it's like force-feeding, against my will and my heart.