...worrying that we are getting too comfortable too quickly
I read your profile. He's taught you to mistrust him. He had a 5 year A and additional ONS. It's too soon to trust him imho--you might end up never trusting him fully. Even trust but verify begs the question of trust. We've learned that lesson the hard way.
For me, WH doing big and little changes are done out of fear that I'll boot him out, although he does have flashes of insight (but they don't stay with him very long). For us, DDay, and TT (DDay#2) feel very recent to me.
A trigger for me is something "concrete" that reminds me of his A or of our M, like a song with words of promise and fidelity, or seeing him be polite to a female who has the same coloring and body-type as the slut.
My gut feeling is an intuition, absent of anything concrete.