How do I go back to trusting him fully again?

As cliché as it sounds, I have the biggest trust issues. If someone wrongs me in even the slightest way (warning another cliché coming up) of course I forgive, but I can't forget.

My boyfriend somehow forgot he was meant to come over to my place, and I was waiting for him but he never showed, we talked it through and I let it go

... sort of. Now I always have this lingering fear, when he is supposed to come over that he won't show up. It sucks, because I feel uneasy and unstable, and I hate that feeling.
How do I go back to trusting him fully again?
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