Hmm, difficult. You were taking things nice and gently and he was keeping his options open. It seems as if he didn't really see you as properly 'going out', but was still open to the possibility.
I suppose he can't have been that keen otherwise he would have made his feelings clearer. It looks like you may have been Plan B, something to fall back on. He was more than likely aware that he was leading you on into greater feelings of intimacy when it wasn't reciprocated but carried on none the less. So for that you have the right to be angry. And yes, I do think he was a coward for just cutting you off as soon as he found someone else. He IS very young though, and probably very immature.
As you get more experienced in matters of the heart, you'll learn to recognise when someone isn't all that into you, and then you can decide not to bother - after all you deserve to be with someone who thinks you're the bees knees.