Right, it is not quite so simple as just having the house transferred. Who knows if Pandora can actually get a mortgage in any event? You cannot just transfer a mortgage to someone else.
Secondly, Pandora is not "buying his house for him". She is properly paying an occupation rent whilst she lives there.
Pandora - you absolutely MUST see a solicitor. You have certain rights and entitlements under divorce law. You may actually be entitled to at least some of the house. The position of any minor children is also very important.
THe mortgage company will go after him for the arrears, not you. The first you may know about it is when Court papers turn up. However, if payments are being made regularly, the mortgage company is likely to accept a small sum in addition to bring the arrears down. This is something HE will have to negotiate with them.