You're searching for answers. Consciously and subconsciously. Your body and brain don't want to go through such an ordeal again. What went wrong? Can I avoid this in the future? Was it something I did? Where was I in the wrong? Can I make peace with anything on my end? All questions that may be percolating.
LH has some of the best advice. Moving on is best. If you cant, maybe there is something you should dwell on for a short time, just dont get stuck on it. Facing what we may have contributed is the hardest part and maybe you need peace there. If you want to know what happened to her....well...why? If you knew what caused her change, then what? Why do you have to know the cause? Likely if your similar to me, it could be because you want your conscience clean. If you did contribute, face it head on and get through it. You've been through worse now so that piece would be easy if thats your case.
You'll find peace in time.
H37, W37 D4, S2 ILYBNILWY 9/19 BD 9/19 EA discovered 10/19 Currently in limbo, no D or S process initiated