My DH and I are allowing his friend to pay rent and stay with us in our guest room until he can move out. All of the furniture in the room,  including the mattress,  is ours. 
 Friend is a bit of a slob, and our guest room looks like a hot mess.  You can hardly walk in the room. I know everyone's got different standards of cleanliness,  but he didn't wash his sheets for months. When DH finally said, look,  you need to clean your sheets,  that's gross,  he took the sheets off,  maybe washed them,  and then... just didn't put them back on.  Or any sheets on. For weeks. 

Again,  different standards of cleanliness, but in the end there was literally no barrier to shield my mattress from this guy's dead skin and sweat. I want him to buy us a new mattress,  but a) I don't know how to approach that and b) making him pay for a mattress is just going to make it harder for him to afford to move out. 

So,  AITA, and even so, should we make him pay for it?