Very good analysis. I agree with a lot of your points.
As with every relationship, how much you both match, as well as timing, is very important.
Objectively speaking, Diane probably had good points to her personality too. But hers and 浩男's personality somehow clashed. The biggest fault in their relationship, I felt, was that Diane did not trust 浩男 (because she did not understand him). Plus, her image of 浩男 must be pretty bad. I mean.. how can she side with Sam, whom she just met, over 浩男, her boyfriend of 4yrs, time after time?!! ..to the extent where she pointed him out in court with certainty as the one who killed Sam.
伊明, on the other hand, believed in him. Even early on, during the course of 浩男's trial, 伊明 was betting with her coworker that 浩男 will win the trial. And remember, towards the end when his dad sent someone to kill her. Afterwards, that private conversation 伊明 had with the doctor in her room.. the doctor asked why she did not want to go to the police, is she afraid that it would affect 浩男. 伊明's immediate response was.. No way, 浩男 would not do this! This shows the difference in her relationship with 浩男, and Diane's relationship with 浩男. 伊明 trusted/believed in 浩男, Diane didn't.