Say what you want, but I really don’t believe there was anything (beyond the building blocks of an emotional affair/safe exit route for Amanda) going on with West and Amanda last summer.
It’s clear to absolutely everyone that they are lying about February, but I think this is the real reason why. Amanda knows she has already publicly shared the timeline of her and Kyle’s separation and stated that they weren’t seeing other people in that period. I think she knows that if they are honest about things happening earlier it will shift the narrative about the Kyle aspect of the scandal since most people (incl. Kyle) seem to acknowledge that it was fine for her to date other people just maybe not West. It’s also possible she wasn’t entirely honest with West about her and Kyle’s agreement, but who knows.
I do think it’s a big mistake (one of a million) on their parts because the obvious lies allow fans and their friends to spiral and question everything about the relationship just out of desperation to make sense of things.