I hope Doubara doesn't become too attached to Mio. At the end of the day, Mio doesn't view their relationship as anything more than a means to reach her son, technically, but I guess in practice Doubara is also the single source of affirmation for her, as others aren't quite as accepting of her idea of the son having been transferred to a new world. Nevertheless, she's not looking for friendship, companionship, let alone anything more. If she actually came to terms with Taiga's death, would she anymore need Doubara for anything? I doubt she would go back to Haruji, the dude being a cheating bastard, but it would be quite a change in her preferences if she went for Doubara. So, Doubara should keep his head cool and concentrate only on helping her and trying to prevent her suicide, but be careful about dreaming of anything more.