It is a very difficult situation you find yourself in and I understand why you have such mixed feelings. However, I would say - what is your main goal? By your presence here I will assume it is for your husband and yourself to reconcile. You can't stop him leaving but you can plant that seed of doubt in his mind that it is the right thing to do. The date is the perfect opportunity.
Do you know what you are doing for your date yet? Dinner, see a film?
I would set everything else aside and concentrate on having a good, fun night out. Make sure you look good, make sure you smell good. Have fun getting ready to put you in a good mood and then have a great time. Relationship talk, him moving out, the devastation to your children can all be discussed at another time.
That would be my advice. Let us know how it goes and good luck.
