When you add in the celebrity murders (by stalkers), that actually creates a significant category of "fantasy romance" murders. And you're right, it doesn't even have to be a romantic attachment (hence the quotes). I've interviewed inpatients where the thought process (as stated out loud) vascillated between extreme attraction/wanting closeness and extreme anger (at perceived distance by the desired object). The murder of Selena Pérez (aka just Selena) can probably stand adjacent to this category.
At any rate, treating psychiatrists often point out that such stalkerish/ragey behavior corresponds to the person's internal loneliness and inability to form regular relationships. This puts me in mind of data we've received (and are still collecting in the social sciences) about the rather radical drop in marriage, sex, and relationship-formation in the current crop of 18-30 year olds.
One of the most comprehensive sex studies to date found evidence of declines in all types of partnered sexual activity in the U.S.
www.wbur.org
This prompted me to give assignments on this topic even before COVID, when it was first noticed. It's young women who are disinterested in sex. Too many hazards, not really important to them, guys just want sex - not relationships/marriage, so why bother? Career first, desire to have children has dropped steadily over my own data collection/teaching timeline. This parallels the Rise of the Incel ( a culture I have been studying for 15 years - beginning with usenet groups and a now-defunct website; there are other websites for this subculture, which also encourages men to exploit and lie to women, as men have a "right" to do ).
These five toxic incel terms have become alarmingly mainstream
aninjusticemag.com
I can give more academic sources, but as this is tangential to the Idaho crime, I think these are thought-provoking and will suffice. This second article is worth a look for those people who are not familiar with these subcultures - it's quite clear and has interesting pictures and quotes.