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.
The people that he's telling aren't supporting you as much as they could be... you could work on educating them more on how they can HELP YOU... don't trust people to know how to handle this well.. Most people are terribly ignorant about this sort of thing... the education just isn't out there... too many hollywood movies romanticizing the whole thing...