Hmm, trust is a very important virtue in any relationship. I refer to it as the pillar in a relationship. Just like a house without pillars will crumble, so also a relationship without trust will not go very far.
It's sad each time we invest trust in people and they end up breaking that trust. It's very difficult to regain lost trust and on this I can relate with you.
I like your strategy of giving people space and time for growth and also for lowering your expectations from people. This helps guard your heart and helping you move on without feeling resentment should anyone fall short of your expectations.