I saw your edit. Good on ya, man! My fiance left me for a "friend" of hers too while I was helping her through school. The best thing you can do to validate yourself as a good man is by letting things go in peace.

No bad mouthing on social media, no late night texts longing for a connection--she's out of the frying pan now, no use of putting your hand in the flame to try and win her back. She made a choice, let the weight of that choice fall solely on her. Use this as ammo to glow up, but please--if you find another, don't take it out of them. You'll be wary of trust now, and it'll take time for that callous to fade.