Lol.
I'm not really a fan of this revelation that supposedly he can't remember any past events unless they connected him emotionally. That's such a vague standard, but the readers can't really follow properly exactly what facts he recalls about his relationship with Kisaki.
I wish they had kept the nature of his emptiness vague, as if he were a black hole that needed certain rare stimuli to actually feel like he's alive, rather than actually mess with his memories. I'm guessing it's going to be exploited to have the story reveal something like "back in middle school, he actually had this or that faithful encounter with this girl here but just doesn't remember because something happened which made him emotionally disconnect from it" or some other memory plot device.
And of course, him actually cheating on Kisaki just because "maybe it would make me feel more emotionally connected to things" is such a dumb idea. In the first place, he clearly is starting to emotionally connect to things in his life more now that he's started to obsess over Kisaki subconsciously, so risking everything going down the drain because he looked at someone other than her and she went ballistic and got arrested or whatever is the thinking of a spoiled child.
But maybe he'll reject this proposal next chapter, we'll have to see...