The girl spies on her sister and engages in home masturbation

Imagine if two sexy student girls share an apartment to save on rent, and one of them brings her boyfriend over, leaving the other girl to either walk in the pouring rain or hang out in the corridor, secretly enjoying the sight of the couple having sex and pleasuring herself with an expensive sex toy. It’s actually quite interesting, but has she ever thought about joining them? That would be really cool!