I don't quite understand - you say you have to live there for 7 years, have been there 4 years yet are free to sell up in another year? If you wait another 12 months, what will you do then? He might still want to keep the flat and as long as he pays you your fair share, I can't see the problem with this. Yes, it was once your home but you have seperated now and need to find somewhere else. If you do wait 12 months, are you on speaking terms or would remaining in the flat together cause problems? If he pays you off then you will hopefully have enough money to get somewhere else where you can start afresh.
Many solicitors do a free hour consultation, it might be worth ringing a few local ones and asking them.