I know that this is a "relationship" split situation so theres a lot more to consider. A lot depends on your finances, whether you are married, whether the "family home" is in joint names, whether you've reached any form of legal agreement - if you haven't, your partner/spouse ( and depending on whether they are joint owners etc.,etc.,) will have a big say so in what is to happen. It won't be a simple matter of using the family home as cross security.
Have you managed to sort out finances between you? I think I recall you mentioning in another post ( and forgive me for the personal touch) that matters were not amicable bwteen you.
I think you need to be talking to a solicitor and also possibly a mortgage broker who should be able to assess your specific situation -as opposed to baring your situation on this board.
Good luck.
mf