The human mind is an enormously complex machine.
I ask the same question every time I trigger or every time a random thought pops into my head or a really weird dream occurs.
My IC said "You can control what you want to think about, but you can't control what you think about. You can't control HOW your mind processes information".
I believe in this wholeheartedly - and consider this: This world, especially in this day and age, is HARD-WIRED for everything sex. I didn't read whether his infidelity was E or P, but either way, imagine all the cues that occur in daily life that "remind" you of sex.
Even if you don't think of it, your subconscious has a way of connecting things - even if you don't like it.
A sight, a smell, a sound, anything can trigger memories, and as much as we would like, there is no way to remove certain memories and leave others. The memory of infidelity will ALWAYS be there.
IMO, triggering, although painful, can be beneficial. Even though it kills me to recall what I did, it also helps keep me in check. Lots of people say "I know I'll never cheat again" but they do. I say it, because no matter how hard I try, I will NEVER get the sight, sound, and feel of my wife crying over this out of my head. I will NEVER be able to look at a woman again without thinking of my wife - and, again, IMO, that's a good thing.
I know it's tough - and it's tough for your H too, but if you made it this far - you can make it through the triggers.
Sending you strength!!
Me: FWH, 42
Her: BS, 41
Married: 15 years
Together: 20 years
Kids: 2 Boys, 12 & 13
"The truth shall set you free, but first it will make you miserable."