Shizuku has secrets, cant break up with Takt cause of what ever reasons, but at the same time wants to lose her v-card with MC, MC managed to keep to his promise and didn't do the deed with her without her explaining the whole stuff - time run out and she moved out cause of the secret stuff.
Umimi seems to slowly get more and more broken - she masturbated with MC hands, nearly jumped and raped him in bathroom, now she is full blown gloomy yanderish with him.
Yako is the only sane girl in this setup and she is like a childhood friend in most romances especially harem ones - aka probably has the least chance to win MC heart - could argue that its good, cause MC is kinda shady himself and/or beta/cuck - and Yako as best girl would be wasted on him.