I really really hate moids constantly wailing about how "being a male is hard and nobody is there for them, meanwhile women are waited on hand and foot!" because it's such a load of bullshit.
Yeah nobody gives a shit about men that's why:
Psychologists and society didn't really give a damn about PTSD, how it affects women and children who were in abusive households and their behavior was just dismissed as mentally unwell behavior, until men from wars would return to their homes and families all psychologically damaged.
Female loneliness has been butt of the jokes for centuries, but suddenly when men get "lonely" (read: cry about women not having to donate themselves to them) suddenly it's an epidemic, every psychologist and sociologist is on the case, we're constantly barraged by slurry of unintelligent articles regarding this topic and women are expected to be sympathetic towards male loneliness, despite men humiliating and shaming women for being lonely.
Society just in recently has reached the consensus that maybe porn is a terrible thing that hurts people, after seeing what damage it does to men (i.e. them becoming hedonistic coomers that spend thousands of dollars on OF and porn subscriptions along with developing insane paraphilias while chasing the coom dragon) , but prior to that any implication that porn is bad and degrading to people was hand-waved as a prude feminazi talking point.
When the topic of predators in positions of teachers sexually abusing children/their students is brought up, people discuss cases where the female teacher was the predator abusing their male students. Even if you try bringing up cases where it's reversed, you're instantly barraged with how the cases of female teacher predator and male victims is more common as if this was some dick measuring contest.
But society doesn't give a shit about men though! Even though all the changes and adjustments are made and tailored for men, even under the guise of "progressive" ideas.
So retard supreme, my sister decided to stay with her bf that she barely likes. The dude is literally waiting for something better to come along. And I don't blame him-- the dude literally cheated on her, and she settled on the motherfucker.
Honestly, not to sound nosy but given this very limited description, it sounds like your sister is dealing with a very insecure but extremely manipulative moid. Usually these types of dudes tend to be emotional vampires that resort to drilling to their partner's head that they're aren't good enough to find anybody else and they are the only person that will put up/tolerate them to ensure their partner/victim doesn't have any confidence to break things off and allows them to get away with them mistreating and abusing them.
If that's the case, I highly encourage an intervention of some kind because usually people stuck in these situations tend to have harder times getting out of it due to denial and low-self confidence.