Look, it's not that I have seen the "introducing a new girl character to make the indecisive girl experience jealousy" plot point a few dozen ti... oh, wait, I have. Three times just this month actually. All of them in yuri manga.
Buuuut, I'm hoping this can be handled in interesting way. Whispering You a Love Song, for instance, recently made the "new girl character" extremely understanding and supportive of her crush going out with the other girl, and that was refreshing to see.
Fingers crossed.