Hey Julia.. GOOD LUCK! Why are you nervous?? I totally agree that it is morally the right thing for him to do, to pay all the costs. I guess legally, perhaps he isnt obliged to, because of the technicallity that he didnt leave the M for her.. but thats not the point right? So look him in the eye and appeal to his better nature and you know what.. screw dbing mentality (I know you said you were too practised already).. but all you can do is BE HONEST. Heck, tell him you cant wait to get on that plane and put all this hurt and shame behind you that you were a bad wife. Say the things you never did before.. that you never wanted this and it was HIS choice to leave and then start an R within weeks of leaving WHILST still being M.. and that therefore, could he just not be an *rsehole one last time and pay for this D !!??? Ha.
But yes, pay half if necessary, if he refuses. Its only money right and you know you wouldnt have treated him the way he is treating you.
As for Thailand.. WOW !!!! THat is so amazing, I am so happy for you!