What is it that you feel is missing?
(maybe you instinctively feel something's missing, but perhaps you're just conditioned to think that... sorry couldn't resist Dramatica joke )
I actually really like your idea for this RS signpost 1 of Memories, where they're reminiscing, talking about the good old days, but then something comes up that doesn't jive with the memories ("wait, after the championship ball game you went to Sylvia's house?" "oh sorry, no, I meant Tyler's house" "hmm...") and there's now an instinctive distrust between them.
That seems to work great for a "best friends -> non-friends (frenemies?)" relationship story!
One idea for Conditioning is to have them trying to do what they've always done, go with the way things have always been between them. But because of this distrust and suspicion, it doesn't work out and causes more problems. (Or maybe, it does calm things down between them for a time--this is where you might bring in the RS Inhibitor.)
Another technique that works for me... You use the Signpost but play it a bit loose with the PSR items, just outlining the scenes however you think would be cool, and look to the PSR for inspiration only if needed. Then at the end you can match things up to the PSR and adjust if necessary. (Sometimes when I do this, I need to change the PSR order to match what ended up in my story. I'm okay with that.)