Does anyone know how to trigger the 'Jerk Friend' storyline?
Or better, have a save for it?
You need to have a good personality boyfriend, not sure what the specifics (in terms of player traits) are but I generally get it with a character with a caring, sleazy, crude boyfriend character. I think it only needs a caring or romantic personality, maybe normal works as well. Once they're your boyfriend it's random chance for him to ask to invite over his friend, then random chance each week for subsequent events.
If you want to genderbend the friend, you need to make sure to refuse and rebuff the friend at every stage, but not throw him out early in the first meeting.
AFAIK, the love requirement was pretty much removed in some patch, even an Aromantic PC can get the scenes.IIRC, the boyfriend needs to also not have either the Doormat or Likes to Share traits. And the PC needs some amount of love for the BF before it will fire. She doesn't have to be madly in love with him, but something beyond the crush stage is required.
Here's the conditions I think are necessary:
Boyfriend with Average/Romantic/Caring personality (Selfish might actually work, not sure, hard to check see below)
BF cannot have Doormat or Likes to Share.
And here comes the annoying part: Relationship strength better than Shaky, which can take absolute ages and there's no real indication of why it won't improve.
As I've never been able to get a relationship with a Selfish guy to go beyond Shaky, I have no clue if that Personality works as well.
Oh and don't marry your BF, that stops the Jerk from appearing, as you're now living with your husband.