1. As far as tomorrow... I assume everyone else important to you will be there... so why would your cell be ON?
Shut the cell phone off... OR better yet, leave it with your friend whom he was talking to... let HER tell him you don't want to hear from him today... I read on a ntoehr forum about a cell exchange like this and it worked out great, both women were having man troubles so they both traded phones... both men got VERY objective advice and criticism every time they tried to call thier respectiev spouse lol
Keeping him from giving up : Keep your ring on Don't date Dont' file Expose his affair encourage friends to counsel him or to be available for him to seek them out - have your one friend tell him he can call her to talk any time.. etc
Your FT that you are both seeing should be able to do this really well, again I can't stress enough the importance of coordinating your actions with hers.. you will have a MUCH more effective attack on the affair if you two trade notes.
NEVER call him back when he calls.. EMail him... ONLY if its CRITICAL to talk... if you can get someone ELSE to leave the message like your MIL, do that.
Avoid any personal exchanges at all costs... email is much more impersonal and safer for you and more painful for him... push the email