Collaboration not working

My ex and I agreed to use collaboration, at my suggestion. Although it was he who ended the marriage we still co-habit, separate bedrooms etc. We have 2 children (under 12)
I thought we were both emotionally stable enough to be ''grown up'' about it but it has all fallen apart & is becoming horrendous.
SO several thousand pounds later I feel stuck, he is uncooperative and verbally abusive whenever the ''divorce'' topic is broached making life at home very difficult as I''m trying to protect our children from his ''bad moods''.

I am considering a court action but am not even sure what this means! I am aware I cannot use same solicitor but before I take the plunge I need to know approx time scale and costs, I really have no idea so the basics here will be very useful.

Thanks x