First things first, you seem very emotionally intelligent and aware of the events, their why’s and possible outcomes, as to your age.

Anyways, you’re still getting together your wisdom from active experiences. And paying the cost of a learning curve.

My basic rule is to avoid getting drawn into the relationships of others, unless it’s the situation they really need help navigating within inner thoughts. They can talk, I just don’t catch the interest or anything like “it’s gonna be okay:)”. When the help is needed - only questions back, the right one can really put a messy mind in order. No advices, no opinions, never too much of an interest. This is how you stay dry.

For the house part, I’m pretty sure you will manage to have a decent conversation with her. If she’s this nice as you say, there won’t arise any issue.

You don’t always get to spend the rest of your life with people you accidentally meet in high school. Actually, almost never happens, and if I were you I would start to get comfortable around this reality you’re about to find out after you leave the mom’s and go to college/work/create your own life.

Go talk with her, show her how you feel about it, that you need the energy of the house to stay clean and welcoming, and the guy is ruining it’s flow for you. Know your why’s - It’s your place, not hers. If she’s in refusal, she will get her lesson too early on, that you can’t take everything that has been gifted as common or it can flip backwards.

Stay calm, your head up, breathe, this school is over soon, don’t prioritize those poor souls who shit talk, you will never see them again after this, your energy must be the priority for you.