Where should I go from here?

So my fiancé and me was kind of forced to live with his cousin in a two bedroom apartment. The apartment is in his uncles name and it belongs to him not anyone in the house. The cousin refuses to clean or pick up after the multiple people he has in and out of here on a daily basis. Two of the men he has had over here peed all over the toilet and bathroom floor and I had to be the one to clean it up. My fiancé just had surgery on his back and is on very serious restrictions so he can’t do much at the moment. But even he has done more for the housework than his cousin even after his surgery. My fiancé refuses to say anything to him and says it’s my place and not his. He yells at me because he doesn’t want to be in the middle of it. I feel like he is totally ok with me being disrespected and unappreciated by his cousin. I’ve even deep cleaned and made the house looks wonderful and 3 hours later the bathroom has hair and water all the place and the kitchen counters are filthy because hos cousin messed it all up. I’m at my end with this and I just need some pointers on where to go from here