Similar thing happened to me I think. W was convinced I had had an affair or was having an affair,although the truth was I was having an affair with my work. I got a buzz out of it and threw myself into it as my W had a pretty hard time allowing me to have much control in my S's life. Only she was right and I wass always wrong, the wrong temp of milk, the wrong way to put him down at night, I couldn't be trusted to sort him out in the morning, at night. I needed to find a sphere of influence in which I was sometimes, occasionally right. That place for me was work and the people there.
My actions around this convinced W I was involved with someone else.I wasn't. However, associated with that was socialising and drinking. All actions I regret and put which put me into a darker place than I ever want to go again. She was also convinced I passed an STD onto her - how ironic!
So I can understand the concept of projection. What to do about it though? I didn't feel I should have to provide a level of explanation as that indicated a lack of trust...but I wish I had looked at everything much more closely at the time and paid attention to what my W was undoubtedly telling me but which I wasn't hearing.
Best - GFI
Me: 40ish W: 40ish Together: 20 ish years Married: 10ish Years
