
Okay, so this is where I'm gonna stop reading. Why would you try to go back to them?

You gotta understand him bro...there are in a war with 5 nations. He's sent to kill the prince whom he fell in love with. The prince nor anyone in that nation doesn't know his real identity yet. In the prophecy, a snake bite will kill him which is obviously the mc. Mc wants to be loved by his family so he accepted the mission of killing the prince but he ended up falling instead. He doesn't wanna kill him anymore so of course, he chose to run away. "Why go back" where else can he go? If his real identity will be find out, what do you think will happen? The prince decided to trust him and now he's actually an assassin sent to kill him. It's basically finding out that your lover is an assassin sent by the enemy country to kill you. Ml isn't a saint and we all know it based on the dialogues and how he was portrayed. Sure, he is a gentleman and a kind person in front of the mc but that doesn't mean he's a good person all throughout. He's not that kind and not that forgiving as well.
If you put yourself in the MC's shoes, going back is the right thing to do even if he'll be back inside that cell. It's called selfless love. He chose the prince instead of what he dreamed off which was having his family accept him. He is in a tight position here and it's very difficult to get out off. If we look into the author's other stories, this one will not not fluffy as it is shown to be. Trust me, this one will go downhill soon and that's what scares me the most...

No worries, you not replying isn't rude or anything but if we go by what you stated, mc doesn't wanna die in the hands of the prince nor does he want to kill the prince. That's why he decided to go back. He's still useful for his family, he won't be killed but instead be held captive again in the cell or be used to kill. They are in a war, his power is useful for them.
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Spoilers
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You see, mc's identity got uncovered and the people there suggested to lock him up and the ml actually did. He became toxic, graping the mc and all. Can you see now? It's better to go back and suffer because you already expected it or you are already used to that person doing it to you. But if he stayed, which he did because he got caught, it hurt the mc million times more because the person who's hurting him is someone he had fallen in love with and who used to caress him softly and assure him with affection. If we put ourselves in the MC's shoes, then we'd be able to see where he's coming from. If I die, I'd rather die by the hands of someone who used to abuse me because that hurts less than dying in the hands of the man who used to touch me with pure love. Dying isn't an option here, mc is still useful as I've said. "After he kills the prince, kill him" or something was the statement of his brother. Which means, because he already served his purpose, he's no longer needed, but in this timeline, he still hasn't because he fell in love. His brother isn't that stupid to kill him when mc is literally their strongest pawn.
I need mokhyeon to finalized the contract with Nanjo and go MIA on his ass Nanjo can have fun with that twink ass!!! He hurt my boy mokhyeon