The voice with Sylvia, the dream demon with Sophiene, the meteor with Epherene, etc.

I don't know how a lot of people don't understand that MC has literally been directly/indirectly involved with the death of their loved ones, hence the fact that they all hate him. If anything, you could praise them for being able to put aside their feelings for the important parts (learning from him, fighting demons, etc.) Just because they've been saved once or twice doesn't erase the fact that he killed their loved one (Epherene's father, Sylvia's mother, Julie's knights, etc.)

Like Allen/Ellie. She became fond of Ducelein and helped him during Epherene's regression arc but after that, she just vanished. She occasionally appeared to help the main cast teleport to places but the conversations that should have been shown about her were just omitted and the readers are only left to assume what will happen.

He slowly becomes one with the character as you can see his harsh tendencies are offset by his gentle actions and in the end, they're practically a new character altogether. Though, I feel like he simultaneously trusts and doesn't trust anyone at all. If he managed to use more of his emotions and confided in any of the main female cast, he might've been able to achieve a different ending that isn't so depressing.

Epherene, Sylvia, Sophiene, Julie, Yeriel, and Lia all loved MC at the end, with all of them having their own reasons. Epherene fell for him because of how much he cared for her despite being her enemy (and being her only ally in the unending stream of time), Sylvia looked up to him as a mentor but over time, her feelings gradually deepened (though she is a bit cuckoo), Sophiene had been with him the longest and he was there during her worst times (a hundred years of regression), Julie wronged Ducelein because she was left ignorant but when he saw the truth behind his actions, she fell for him. Yeriel, despite being one of his greatest enemies/threats to his life, was unconditionally loved by him as his sister. They weren't of the same blood and the one flowing through her veins was threatening enough to even get him sent to the gallows. He (Kim Woojin) fought himself (Ducelein) to accept her and the two came to a consensus. Lia, or to be specific, Yoo Ara, since the character Lia had absolutely no reason to fall for MC (assuming that the original Lia doesn't have the memories of his original fiancee) regretted being that way with Kim Woojin. Her only wish was to get out of the game world so she could be with him again. Finding out that he was actually sacrificing himself in another world was enough of a reason for her to even give up her chance at getting out (the ticket) but Kim Woojin refused, stating that he didn't want to live in a world without Yoo Ara.

Not feeling longing for the rest of their lives (and not dead).