If he's so easy to talk to, I would tell him the complete truth: that you are nursing a broken heart from a guy who lied to you and hurt you deeply.... and you had a knee-jerk reaction to protect yourself from experiencing the same type of hurt again. Tell him that you're deeply embarassed and that you will try not to do it again, and the he'll be the most wonderful man on earth if he gives you a second chance, some understanding, and a little patience.