Remember one of the golden rules: don't mind read. You don't know what he thinks. Don't base decisions on mind reading. Now to answer your question from my experience, my W thought she was getting away with the A.
I completely understand the fear...the fear that he will file for D. But you can't let fear run your life. You are stronger than that. Most of us have been there with the fear, letting go of the fear is hard, but in the end, most find it very reawarding. Big relief for yourself personally when you stop letting the fear run your decisions.
I'd call him on his telling people at work. Remember, you are in the right, you are on the high ground, he is having the A. Think people at work won't put 2 and 2 together? It is announced you two are splitting and he is spending a ton of time with OW. Hmmm....
You can maintain the high ground and not say a word and people will figure it out. I wonder if he would actually go through with telling people. Many co-workers probably already suspect something, they are smarter than you think. I only ever confided in one co-worker/friend that W was having EA and he immediately said let me guess it is XXXX. And he was right. He said he always felt there was something more than should be going on.
M39 W41 Two children WAW bomb dropped 11/7/09 Piecing Aug 10 - Nov 10 No longer piecing...Nov 10 Separation Jan 11 EA ends again Feb 11 Piecing attempt #2, Mar 11