You don't have to have a specific scenario in mind to talk to the solicitor. Simply a few questions:
My ex offered to buy me out of our flat but has now backed out of that deal. I'd like to list the flat for sale. What are my options to force a sale? How much would that legal action cost me?
Must I continue to pay part of the mortgage to keep my rights over the property? I am currently living with my parents but would like to get another place and can't afford to do so. How would stopping paying my share of the mortgage affect the amount I would receive after a sale?
I left the property on XXXXX date. Do I have the right to move back in?
I think answers to these three questions would give you the information you need for you to decide what to do next.
He could drag this out forever, you know. Especially since you're basically subsidizing this continuing to live in the flat.