How do you learn to trust someone? (preferably from people who have actually done this)?

I love my ex-boyfriend. When answering this question please keep this in mind. I don't want to sever our ties, but I'm afraid I'm going to have to. We broke up recently but unhappily. Neither of us did anything wrong, we just had a difference of opinion about an important subject. Our biggest problem is probably my lack of trust and his issues with being honest (which are obviously related). He is scared to be honest with me about some things because he thinks I will get mad (which is probably true), but I think he also likes to have secrets from me to keep things interesting. I have an incredibly hard time learning to trust him now because he has lied so much in the past and does occasionally even now. People say that a relationship is built on trust. If this is true, then ours is lacking the foundation. We have no trust - both of us are jealous, nosey, and most of all stuborn. I want to trust him, but how do I get over his lies and get him to be honest with me?