This theory is completely possible, especially of the break/ breakup was on the cards perhaps she told him she needed more time/ decided to go on her own and he blew up. Hung up and then she in a fit of sadness, dispair and loneliness decided to carry on a bit longer, getting into difficulties and perhaps perishing.What if it was something like this:
They had a blazing row during the final WhatsApp call. He said unspeakable things to her in a fit of rage. Slammed the phone down. He's now boiling with rage and she's completely discombobulated, upset, flustered, crying, feeling like she's worth nothing, almost to the point of self harm (therefore not so careful with where she goes next). She goes off walking, westbound, in this state, and because she's not being careful or sensible. She climbs something she shouldn't have, almost reckless in her abandon, has a horrible accident and dies.
During all of this he is at home in France, boiling with rage, doesn't care if he hears from her or not. Could THIS be the reason he waited 3 days to call the police? Maybe he needed to calm down and for his rational brain to kick back in again before he saw sense?
Could this be the reason for his shifty behaviour with all the red flags, plus his need to control the narrative etc?
Doesn't explain the "loved" comment, the wrong search direction or him miraculously finding the body, mind you. Each one of these can be explained away, but all 3 together make it dubious imho.
We all know it doesn't add up, hence the massive interest in this case. We just don't know "why". Sadly I doubt we will ever know what truly happened.
Meanwhile he decided that he would ignore her for a few days and then try and make see" Sense" good theory i like it.