His ex-wife is living next door

He should have talked it over with you before letting the next door property to his ex! How could he think that would be ok? And what on earth does she want to be there for? You should tell him how hurt you are that he did this behind your back, and that he has now put you in a horrible position. It just puts too much of a strain on your home. He should promise you a deadline – that she will move on asap. Then he needs to have a meeting with her and, without blaming you, tell her that the let is only temporary, he has someone else moving in on a certain date, and she needs to move on.