My theory is that he's a very closeted gay man. I don't think rejection of him as a potential partner was a trigger. I don't think he wanted women, other than as prey. In his day to day story line women were a vehicle to what he considers to be self-elevation. He accepted social cues from men, apologized, left, didn't bother anymore when asked, and so on. But he took the time to argue and put down when interacting with women.

He's clearly on the narcissistic spectrum, which is kind of a loop of self hatred and the inflated ego of main character. He studied himself in depth, but in the way you study a deity rather than to find cause to his issues.

(Saying that someone killed women because of rejection veers on victim blaming, which I know you don't mean but verbiage matters.)