Well, the way I see it (which may be wrong): the situation with Yumi feels forced as it is. But it's intentional, and Selebus plays around with the fact that it's forced. Because any game where you end up with 500 women, it's gonna feel forced. That only happens to kings and warlords, not even the most "super awesome super likable guys". The game highlights that MC doesn't really deserve any of this and everyone is being pushed in that direction because they happen to be characters in a harem game.
Not really in the same context. It feels forced now because it is, she doesn't want him to butt into her life, but he's doing it anyway because she needs it if he is ever going to get any closer to getting with her. What I meant by forced in my comment is that the situation was written in a way that there was no way for it to feel natural at all. At least forcing a stubborn girl who doesn't know how to get out of her rotten situation is a kind of force that feels natural. If Yumi wasn't the way she is, yes, it would feel forced in the context that I meant in my comment. No, unlike most harem games, the characters in LiL are not being pushed by that fact into being with him. Case in point, Rin, who went from liking Chika to starting to like Otoha, which she still does. There is only one instance so far that shows she might be falling for player Sensei, but that could easily be written off as a mistake in judgement at a highly emotional and vulnerable moment by Rin.
In this case, it's specifically discussed in one of the 15.1 scenes. It feels forced because it is, not just externally by the author, but internally by the scenario. It's discussed as a clue to what's really going on (which still isn't being explained -- fortunuately -- but is becoming increasingly alluded to)
Her situation pretty much requires a forced situation, no other character in the game is this stubborn about her own problems and not accepting outside help. She forced player Sensei's hand.
Big reason I can draw is MC being "hot single MALE in your area", with the war taking all the other male away(plot), active female are either gonna get interested in MC or choose to be les for their partner.
He's not the only male exempt, just the only one on screen that is. I'm pretty sure Ayane's father is also exempt, likely bought his way out. The space war did take 99.9% of the male population away, leaving the female population to go after the remaining 0.1%, which includes teachers and other essential non-combat personnel like player Sensei. His profession is what got him out of the war. That is a big reason the girls are going for him, but then you have outliers like Rin, who has fallen for not one, but two girls, both in player Sensei's class and both right in front of the guy. She has made one move in his direction, but that can always just be written off as a mistake by Rin. It's not like it was anything irreversible, after all.