Honestly I find this more confusing that everything. Wistrash is just a poorly written character.
Sure “I don’t love you anymore” is a powerful line, but what garbled characterization Wistrash has tells me that he wouldn’t care or be particularly shocked that she no longer loves him than he cared about the fact that she loved him back when still felt that way. It seems baffling to think that he believe she would stay with him forever because she loved him, since he seemed to barely register her emotions rather than taking them for granted. He straight up call her feelings “trivial emotions” in an earlier chapter. I would expect him to be trying to argue something like “you’re acting irrational” instead of “this is so sudden, I don’t understand.”
Etc., etc. Overall, Wistrash is a mess of motivations and actions that are in conflict with another, and in “this character is poorly written” sort of way, and not a “this character is well developed and feels like a person” sort of way.
Wistrash feels artificially put together for the sole purpose of being such a neglectful, indifferent shit bag that he drove the FL away, yet still somehow possess enough basic empathy and desire for her companionship that he feels bad about how he treated her and is heartbroken about her leaving.
The only reason I haven’t dropped this series is because that is exactly what I’m here for lol.