Do another skim read through the diary and notice all the times he unabashedly confirms his belief that other human beings in his life exist to serve his interests. It's practically a motif. He doesn't merely seem upset that women won't acknowledge him, but rather that anyone he interacts with has any agency at all --- his father, his mother, his friends, his roommates.

It is a mixture of psychopathy and megalomania. He expresses a belief that women exist to provide men with sex, and his anger stems from a belief that women have been given the power to choose who to have sex with yet failed to choose him. He believes that he is better than everyone else and is angry that women are having sex with "inferior" men. He does not think killing other people is a problem; he thinks that his own death is the worst outcome of his plot, made necessary only because the alternative is to live in a jail cell. He also describes killing his roommates as necessary, lest they get in the way of his plot (which included torturing people in his apartment).

In his ideal world, there would be a benevolent dictator -- "benevolent" in this context includes exterminating women by starvation, save for a few that are kept locked up in labs where they exist only for reproduction -- and he suggests himself as this dictator. According to his theory if there are no women there will be no sex, and men can rise to higher levels of achievement (notice how he blames his shortcomings on others). He also believes that there would be no love in such a world, though he seems to have a poorly developed notion of love as an emotion (he speaks of love in terms of sex, and never associates love with any specific person other than himself).