I'm pretty sure Adachi broke up with Tachibana because he thinks that Tachibana will get hurt by being with him after seeing his stalker push Tachibana down the stairs. I'm not sure why he's with the stalker now but in one panel you can see him holding what I'm assuming is the letters the stalker sent so maybe he's confronting her or getting blackmailed or something??
Plus Adachi heard when Tachibana said to his ex while laughing "Yeah, it's not like you fall in love with each other just because you start dating" or something along those lines
I'm pretty sure Adachi broke up with Tachibana because he thinks that Tachibana will get hurt by being with him after seeing his stalker push Tachibana down the stairs. I'm not sure why he's with the stalker now but in one panel you can see him holding what I'm assuming is the letters the stalker sent so maybe he's confronting her or getting blackmailed or something??