My roommate has officially moved her boyfriend into the house

We supposedly moved into this house as two people, but the girl's boyfriend stays with us five days a week now. The kid literally sprawls in the kitchen and occupies the bathroom for hours, I’m really uncomfortable with this situation. I told my friend once, but she just says, "We're going to get married anyway, what's the big deal?" It's like a joke. We’re the only ones paying rent while he’s living here for free.