Welcome to the forum karabat
I'm sorry to hear you've experienced such overwhelming disappointment. Such disappointment definitely shapes our thoughts and relationships.
Perhaps it's worth looking at your definition and conditions of trust. I must say, personally I'd never thought of doing this myself until now so it's an exercise I also face...Okay, to get the ball rolling, I've just looked up an online dictionary and had no idea there are so many definitions in relation to trust.
I suppose what it comes down to is responsibility and integrity. Whether we're dealing with a financial institution which helps take care of our money or we're dealing with a close friend who helps take care of our well-being, both are entrusted with a certain level of responsibility and integrity. Such trust ultimately provides us with a sense of security.
When we entrust our riches to another (those of our heart), we're appointing great responsibility. Sometimes those we trust will disappoint themselves from such a role, in a number of ways for a number of reasons. We can be left to feel the disappointment deeply. 'So, who can I now appoint?' becomes the question. If we're surrounded by people with questionable integrity, who are not up to the role of such responsibility (in safe guarding our heart), then we find we can't really trust anyone. We become cautious and understandably so. As one person after another is assessed in the way of trust and found to be lacking, the message 'I cannot trust' is resent to our brain over and over again. Hence, the resentment.
Instead of focusing on the message being resent, try focusing on the folk around you who are proven to have great integrity, those who are also highly responsible. Can you think of any? If not, don't be too concerned; such people have a way of coming into our life at different stages. They can be like rare gems, few and far between, but they do exist. Of course, level of trust is a factor. Whilst there are those I can trust with certain aspects of my well-being, I may not be able to trust those same people with very personal pieces of information and that's fine, I've learned not to appoint them that role, 'Guardian of secrets'.
All just food for thought karabat.
Take care of yourself