I'm not sure, but I think that the NPCs have a stat, "attention", which is daily increased b 5-7 points if they don't sleep with you. Once their attention reaches 50 points, the NPCs are "eligible" for a personal event: the game picks one of them and compare their attention to a random number between 30 and 150. If their attention is smaller, the NPC has a personal event and its attention goes back to zero.
Again, I'm not sure and I didn't make any test, but you may open the file "files\scripts\Mansion.gd", find the line:
if personlist[number].attention < rand_range(30,150):
and play with those numbers. Remember to save in UTF-8 format. Backup the script before editing it.
Eta: in the same file you may also play with this other line:
person.attention += rand_range(5,7)
About the text editors: Notepad literally can't into line endings. Go with Notepad++. Or, alternatively: Atom, Brackets, Sublime, Scite.
MS Wordpad sucks too (can't deal with UTF-8 encoding). Avoid also MS Word / Writer for stuff like this: they will fill your files with sh*t. Good luck!