I think you need to have another discussion with him. Find out if and when his wife is returning - are the children of school going age, if so there must be some valid reason for taking them out of school for so long , perhaps they are separating. Is he availing of the Revenue rent a room - if so he will get the rent tax free while you will have to pay tax on his rental to you. Who is responsible if the new tenant had an accident in your house. You need to sort all this out and then decide. On the other hand he is being upfront with you so perhaps you can do some sort of deal with him.