Premed student wants wholesome girlfriend who's a virgin (like him i assume) for long term relationship, then (likely gold digging cuz future medical doctor) cheating ho girl lies and says she's a virgin despite banging 10 guys before him and actively cheats on him, then he snaps after seeing his girlfriend cheating on him and learning about her true wicked nature and he's the bad guy? Girl played with fire and got burned, thats on her. And the girls in this manga called him a cuck as well beforehand, like how much abuse is one person gonna take before he snaps?
Also if the genders were reversed I'd say the same thing (ex girl premed student, guy cheating scumlord)
https://tenor.com/bh47v.gif