I wrote an article on how to gain a persons trust, now how do YOU learn to trust again. So you've been let down by others in the past, and this has hurt you deeply? A lot of what applies to gaining a persons trust, is pretty similar to you yourself learning to trust again. Except it requires more of an open mind.
Give people a chance. It's easy for you to compare a person, or relationship to one in the past. Even if this is the person who broke your trust. Not everyone is the SAME, or aren't willing to learn. You can't continue to think that way, otherwise you are never going to be able to give anyone a real chance at trust. Everyone at least deserves a chance, so be fair, and give them one! Don't use the past as a reason to not have an open mind. The past is the past, you are in the present.
Communicate with them effectively. Similar step to gaining someone's trust, it's the same thing with gaining it for yourself. Being able to communicate effectively, and really talk to one another about each person's most inner thoughts and feelings.
Learn more about them. This doesn't mean just specifics, like where they grew up, what is their favorite color. Learning about them, and what motivates their feelings, emotions, and desires is very important step in developing trust. You can't really begin to trust someone, until you can truly understand them. Actually, until you get to a point where you can predict what they'd do. Really examine who they are and learn about them. Write down situations, and see if you'd know what they'd do, or what they wouldn't. If you don't know, you don't know them well enough to trust them yet. Keep learning about them.
See how they treat others. Very important factor in figuring out whether they will deserve trust, is how they act and treat others. How others who know this person, act around them. Are they the kind of person that seems to bring out a lot of warm feelings in others? Or are other's a bit put off with them?
Everyone makes mistakes. Giving second chances is okay. Really determine why a person broke your trust. Really understand the situation and put yourself exactly in your shoes. You got to understand what triggers a lie, or why someone would betray you. Sometimes people do things out of fear, not to hurt others. When you make sense of it, and then try to show that same understanding in return, it gains trust for this person. Which in return will help you allow to trust them in the future. Where they'll truly learn and grow from the reasons.
Are they a learner? This again applies if you've learned who they are as well. Are they the kind of person that listens to others advice? Are they the kind who truly grows and learns from mistakes they've made? If you've discovered they're not, then you probably have your answer on whether betraying your trust has truly sunk in enough, where they won't do it again. Some people feel bad, but it doesn't mean they ever learn. Learners deserve another chance. Non-learners don't. Figure out if they're a learner.
Avoid giving trust to self-centered individuals. This is the biggest sign, on whether or not someone is worth giving trust to. If they're self-centered to the bone, then it's a 100% chance they'll betray the trust, or do it again if they already have. Unless they can honestly learn to be more selfless(which is pretty rare), then they are capable of trust. Don't read too much into this, because a lot of people have selfish tendencies. In fact we all do at times, it's only human nature. What I mean is, do they literally never, ever, take time to really think about others needs? Do they seem to just not really care? That's a self-centered person, where they are only motivated by self interest. Which means they'll do whatever it takes to please themselves. That includes lying and not being honest with others.