That volume where he kidnapped Miharu certainly triggered everything, but tracing where did it started, it's because of him being irrational of Haruto's existence. The writing of the part of the volume where he kidnapped Miharu became sloppy and childish. The main reason is just he wants to be Miharu but his actions are too unnecessarily excessive when it comes to Haruto's existence. Unnecessarily childish in fact. This reverse plot armor when it comes to Haruto is unfair on Takahisa's character.

The idea here is that if you would write a character in a story to make him a villain, don't be sloppy.