Who can you trust?

My parents always say I am simple and easily trust others. I had been always believed that one should trust others first before asking for others' trust. However, what happened to me lately really made me doubt about what I believed.First, the man I married for over 20 years ruined my fully trust, which ended up with I showed him the door. The second thing happened to me was a co-worker whom I (as well as all people around) considered as one of my best friends stabbed me in the back while sending his feedback on my performance. He put a list of un-true things there. It was anonymously performed and he thought it could not be identified. Fortunately or unfortunately, he was the only one put such things there comparing with the high marks from other colleagues, which made it easy to distinguish the source. Now, I wonder if I can trust anyone?