You want to know what pisses me the fuck off? DISRESPECT. My 24 year old sons girlfriend who basically does nothing all day every day essentially lives in my house and it makes me want to vomit. She's here 5 days a week. My son is in health care and works 2 overnight shifts a week, for now, and she just lays in his bed all fucking day and then is awake all night consuming food and alcohol. I have a wife and three kids in a pretty small home and having her here is not ok. She has a big home barely 5 minutes from here. My wife doesn't want to upset my son so she tolerates it. I don't understand, is it only me?
It's not just you. That just makes me think of some people I knew when I was that age. You're situation is no different than how those people were in the relationships I have seen from my cousins.
Does she even contribute any help around the house, like cleaning, doing dishes, going to get groceries, offering to cook, those sorts of things? IF I had a child, shit, If I had a significant other that didn't contribute to help around the house, especially if it's my parents house, I would've said something, and my parents would've definitely told her something, at least they would've let me know of the situation and gave me hints to say something to my partner.
IF I had a child, I would also talk to them about this situation, and maybe relate that if she's like this around the house now, will she be this way if you two were to move in together?
But the way I see it, it's your home, and if you feel she's not doing her fair share of helping around the home, you're free to kick her out. Your son may not like it, but he also should understand your situation and how it effects the entire household.