If he is anything like my H was the "being nice" is an attempt to get you on board with mediation and get moving on making the appt. When he doesn't get his way he starts an argument. Do NOT react to his arguments. Have a PMA and go about your business.
If he keeps pestering you, let him know you have no intentions of calling the mediator as it is not your desire to divorce. If he chooses to initiate a divorce you will respond as the law requires you to but otherwise you will not willing participate.
If he gets upset that is his emotion to deal with and own. Do not allow him to take it out on you. The WAS has a grand plan for how the divorce *should* go yet fails to alert the LBS until all the decisions have been made for YOUR life. It's unacceptable and he set the tone for that, not you.
