You shouldn't turn against people.
Selma used to be friends with one her coworkers but now sees that their boss doesn't like the coworker much at all.
Selma wants her boss to think highly of her.
Selma stays friend with her coworker and convinces her boss that the coworker is actually great.
Selma stops hanging out with her coworker and starts being cold and distant with her.
Selma's coworker doesn't have problems with their boss anymore and is grateful to Selma.
Selma's coworker feels sad and betrayed.