Okay then, simple. Just phone him, don't text him - they're too easy to ignore-, tell him you wanted more than a platonic relationship with him, but misread that he wasn't interested in you and decided to try to get over it by going out with man #2. Tell him it was nothing more than a simple drink / dinner- whatever it was- and that you'd really like to be going out with him. If he's a sensible human being he'll take that on board, if he's not you've had a lucky escape- either way life's too short.