ML unilaterally wanting to protect the MC even though the MC really wanted to leave everything behind to join him and wasn't some snot-nosed kid; he made the decision with full awareness. These kinds of breakups seem more common in CN stories where people hide things and lie to family members in the form of "protecting" them.

it was strongly implied that the MC would have been way more happier making his own way with the ML and building business empires while being together. Instead, the MC suffered through a decade of loneliness and being mentally/verbally ab*sed by his awful father and working for pennies for his awful dad, wasting years of his life. He also suffered from sabotage and near-mu*der working in his father's company.

Eventually he leaves his father to start his own company, but one can't help but think how he would have been so much happier if he'd done that much earlier.

the ML had grovelled a bit more for his unilateral decision back then. He also didn't do anything you'd expect like apologize to the MC for breaking his promise like a few days? A week? After they had gotten together and him agreeing when the MC said they should be together forever.

I get that the ML felt like he was dragging down the MC and didn't want the MC to suffer with him, but guess what? The MC suffered a shitton anyway! Which always happens when you make decisions for other people!

the ML isn't to be blamed for wanting to protect the MC. I liked how he, unlike other CN MLs, knew his behavior was stalkerish and bad and he tried very hard to maintain boundaries, work on improving his psychology, and not stalk the MC.