The wiki is gone, but the wiki explicitly stated that if your boyfriend has the LIKES_TO_SHARE trait, it blocks off that specific line of events. The reason for this is that the eventline has all it's scenes written with the assumption that your boyfriend does not have that trait.
It's another one of the eventlines that's horribly under-written. LIKES_TO_SHARE doesn't have it's unique content in it yet and you also can't actually leave your boyfriend for the jerk friend yet either.
The Boyfriends_Jerk_Friend event chain can be blocked by a whole range of things...
It can't fire if the boyfriend has either the LIKES_TO_SHARE or DOORMAT trait and/or the Jerk Personality, not quite certain, but Selfish personality might block it as well.
Also, you need to have been with the BF for a few weeks and he needs to like you a bit, AFAIK relationship status needs to be better than shaky (aka good or close).
Since he needs to like you, MISANTHROPE probably blocks the chain as well, but COLD_HEARTED does not anymore, as the love point requirement was removed a few versions ago.
The only unique content for LIKES_TO_SHARE I can think of right now is the reaction to the Blackmail event you already mentioned, also you get a similar reaction if you confess cheating via serious talk (as in, he gets horny and takes you to bed) and he's always up for a threesome.
Oh and if he's got the CHEATER trait and you're married, if you catch him in the act and confront him, he'll be annoyed at the interruption and tell you to go fuck other people as well.
That actually reminds me. A changelog stated that you can now trigger walking into the men's locker room on accident even if you start as a woman. I forget what that scene actually involves/leads to and the wiki is gone, so I can't look it up there anymore.
If I remember you need to be SULTRY to go into the male changing room. That leads to either having to dance for them or flirting with one which in turn can lead to a shower scene.
These are different scenes.
The one FrogFrozen refers to is the accidental one, here's the blurb from the relevant changelog:
Following a PM on patreon, relaxed the conditions to accidentally walk into the men's changing room at the gym. The request was to add a new trait to enable it for female-start characters, but instead I've decided to unlock it for any forgetful character who is not also perceptive. Non-forgetful gender-bent characters can still access the scene at low femininity, although perceptive will still prevent them from making the mistake.
Probably depends on your character's personality/traits a bit, maybe on the main guy in that scene as well, but generally you're asked to do a little sexy dance so they don't report you and that's pretty much it.
The Sultry version is just your character consciously deciding to walk in there to fuck around.