I would strongly reccomend celebrating withOUT your huband's involvement.
Back to my earlier point though, as your husband exposes his affair as a mere friendship, you need to combat that as exposure of his affair... NO one is going to believe HIM if YOu are telling everyone he's lying and that he's sleeping with her.
You need to get the word out on two points :
1. My husband is sleepign with this woman, he's lying to you when he says' they are just freinds. 2. I WANT my MARRIAGE. I need HELP from everyone to PRESSURE my husband to END the affair and ACT like a RESPONSIBLE PARENT and HUSBAND. PLEASE INTERVENE and TELL them both you are ashamed of them and that you don't want to be AROUND THEM.
Yep -- BINGO. This. ^
I would advise you to stop monitoring his cellphone usage, or perhaps discipline yourself to check it 1x/week, save the data, and then wait another week before peeking. It's not confirming anything you don't already know, and it's messing with your good PMA and GAL.