Are you sure you aren't looking at things with rose-colored glasses? Or else why would you threaten to leave every time you got into an argument? Are you sure you were actually happy?

And if you were and were just threatening that, you've got to understand how frustrating that actually is. Imagine anytime an argument arises, you go through the heartbreak and confusing of a breakup, and then are back together and meant to act like nothing happened. He's going through a rollercoaster of emotions, and you seem unstable, unsure and immature.

Don't go back to him until you are sure of yourself, sure of these things. But your threatening a breakup at conflict raises some red flags about either you being ready for a relationship or you being right for the relationship.