I'm not going to give you some cliché answer that your friend might give you post-break-up. I won't say that he wasn't good enough for you, or he sucks or he doesn't even know what he's walking away from. Those are fine things for your friend to say if they are true. It's awesome to have great friends who give you encouragement in that crappy moment.
But, I'm not your friend so I'm going to give you something better. A takeaway for your next relationship to end differently- or not at all.