You can break down and have a good cry after you leave if you need to. Put on a positive front. 'Fake it till you make it' if you have to. Make sure hair and make up are done and you have on something that makes you feel good. Those things always help when trying to put forth a PMA.
If the family is going to say anything at all to your H about you, you don't want them saying what a bad guy he is out of pity for you. You want them to say, H you're a fool for what you're letting get away. Make sense?
If you don't think you could handle staying for a while tell your MIL that you have plans and thank her for asking.
You've got a few days. You can get yourself ready for this. You'll find strength you never knew you had. That and patience, lots of patience.
