there was a time for a while when we first started going that he was still seeing the OW and pretending like he wasn't, and working on the M. Then I found out (through his cell bill) and once again I was devastated.
Yep BTDT myself. My H went online the December after I had our son. We began MC that following June...so June 04 through Feb 06, my H was cheating on me online. Fortunately for me he never met anyone physically...but the pain of the betrayal was horrendous to say the least. But as you can see...he also would go to the MC sessions and make SOME progress when it came to communication etc. But he withheld what he was doing the entire time...until I, as you, discovered and blew that secret out of the water.
Your H NEVER should have been hiding the cell phone records from you after your Dday. You made your discovery through the cell phone records...so that should have been a given that he needed to provide you with those and not continue to hide them. I'm sorry sweetie, but that's a serious red flag to me. His continuing to do this AND his little deflective/defensive temper tantrum the other night fits neatly into what we call "gaslighting" during a wandering spouse's "fog". God I hope I'm wrong about this, but I believe there is reason to suspect he's doing something.
Your MC knows that you found out through the cell phone bill right? Even if he does, he might need a reminder if you haven't already given him one.