To an extent, the fact that he has (evidently) been able to make it work with someone else demeans your every criticism of his erstwhile behaviour and conduct. How can he appear to have his cake and eat it too? Were you, perhaps, overly exacting; and what does this augur for your subsequent relationships? If we were basically incompatible, why did we ever enter into a relationship in the first place? How come she can tolerate what I couldn't? You'll either envy her for exhibiting a forbearance you never could, resent her for harbouring an affinity (for him) you never did, or hold her in contempt for compounding his denial. You'll pity her and disdain him for having clearly hoodwinked yet another impressionable lass, or, alternatively, for treating her with an affection and deference that he never conferred on you; which scenario seems no less unjust nor a damning indictment of his character. You'll begrudge him his having seamlessly transitioned into a new relationship, when you are acutely conscious of your own residual infatuation; despite that his experience has been, in all likelihood, quite comparable. Then, when you meet up, with doubt cast anew on your misgivings, you'll be as suitors once more; except, unlike before, he'll be spoken-for.
In any event, insofar as you decide to dwell on it sceptically, any comparison seems inauspicious. Just move on.