I agree that Yami made a tasteless and dangerous decision when she ordered a john for Hikari. But I think it's worthwhile to understand the context in which she made that decision. She's dealing with trauma and mental health issues, and she's coping by pushing people away. Hikari kept pushing in despite Yami's obvious attempts to keep her distance. So like a wounded cornered animal, Yami lashed out. I think that's very different from a true psychopath who hurts people without context. I could forgive Yami for it, but I wouldn't want to keep her around if she doesn't make an effort to change. Same with her impulsive hook-up and situationship with Yuu. She broke his heart, but there are reasons.
Ayami was a formal girlfriend for Yuu, and he calls her "my girlfriend" already during those morning in the love hotel after their first time in chapter 4 of his PoV in the Web Novel.
And you are exactly explaining why Yuu doesn´t pressure Ayami about her mental heath issues.
He was following a strategy of going slowly but certainly, to try to heal and fix her. He realizes very fast and very well, instead Hikari would do in the future, Yami always will lash out if you pressures much to her. In this case, his cowardly was fully justified and he was and is still right.
Yuu definitely pressured her to having a formal and romantic relationship, and is implied he needs a romance to... work it. Hikari was right about him in the most literal way, the boy needs feel he is a romantic relationship to have sex, without it, he literally doesn´t works, he needs romance to be arousal. Exactly like Yuu Izumi.
Again, Takamura is Izumi, he is much more interested on romance over sex, even if he obviously won´t refuse a sex offer. In chapter 4 literally we even have the typical scene of the girl asking the boy in bed "what are we?", but with the gender roles inverted.
Again, Yami-Yuu relationship is a role reversal relationship where the "man who carry the pants" is HER.
Because they are basically Yuu Izumi and Ai Kamiya dating. This is the If Route of Kamiya. And yes, this is the reason why he accepted follow her to the love hotel. In his mind, he believes he is getting a girlfriend.
And the best part it is he was right and Ayami accepted being his girlfriend as later in the chapter 25.5, when she sees him sleeping and kisses him in the lips, is very obvious this is the point when she accepts she is really in love with "this weak coward".
Yuu is so chad he reached to see how Ayami were falling in love with him even before herself. Yuu really got the loyal and loving girlfriend he always wanted, this is the reason why he is so broken after breakup with Yami, breakup, again, provoked by external locus reasons he couldn´t control, even if he probably pressured Yami to met her mother -this ironically could have helped to avoid the suicide attempt of Ayami mother, at least maybe-
For that in all those chapters 26-29 we see several love declarations between them and how both treats their relationship as boyfriend and girlfriend, literally.
And yes, this is the reason why the rooftop scene in Shikimori-san basically implies Kamiya cannot live without Izumi to her side at least as a friend (and this is the reason why Miyako is so empathetic with her here, because she as a yandere feels the same by Izumi