He said not deserving not trash. What is this twitter take that "you like pancakes so that equates to you hate waffles" sht. They are not tossed away, he saved them and now he want to live his own life and find his own romance and it sadly doesn't involve them. Nobody wants a traumatised baggage. Why do people say "move on" when girls choose someone else but when guys do it "it's tossing aside". And I would have understood if he was in a relationship, no they were friends. He saved them, he did his best as a friend while all the others did was traumatize him, he is better than all the rest combined. Now as he has done his job, it's his right to move on and go to greener pastures of his life unburdened by the baggage of the past. It's not his job to suffer alongside them.
Of course the suicidal mission is sht is tyrannical level of pettiness but that not what the original commentator was saying. He said if he found his own heroine which is well enough deserving wish for the Mc. You think a hero who sacrificed everything of his life, saved the world, became a king didn't deserve and will probably find a good enough VIRGIN heroine? Now that's a virgin take. Even the author probably knew that people would call out this bs so he made the whole time line and reincarnation bs. So, move on.
To be fair at that point Ark's only picking up Yuuya's sloppy seconds, his well-used sloppy seconds. Even if Ark has any lingering feelings for Shou or anyone else. It's weighed down by all his trauma from everything that happened. Still, I say it's more a concept of pain and penance.
He had to take the abuse of the Fake Hero, his sister, childhood friend, the healer he had a crush on, and his own fiancé. Who were all banging the Hero without care of him knowing. Mind controlled or no, they hurt him. Humiliated, neglected, isolated, cursed, and toyed with him and his feelings. With the fake hero either dead or practically so(thanks to the girls). They honestly are the only ones who can bare the weight of his wrath or answer for the fake's actions.
After all he's been through he's just done with them and never wants to see them again. They on the other hand are so thoroughly broken mentally, spiritually, and emotionally. They want to die for how they treated Ark. Shou/Xiou moreso than everyone else. The self-loathing is beyond comprehension.
Knowing all romantic routes are dust and destroyed, both Ark and the girls resign themselves to a strained and limited relationship of King and Slave. They'll accept any request from him no matter what. Because this is all that they have left of their connection to each other. As well as the only thing they can do. Ark's pissed and isn't ready to forgive anything. The girls are suicidal and want to be severely punished for what they did. So lethal missions for life...