In line with the current trend of "much maligned and long suffering wife finally asks for a divorce, and her formerly cold husband realizes what he's missing when she's gone" stories.
This one sets itself apart by adding a mu*der mystery and seems like it's going to make the FL a badass.
The deal: the FL actually was pretty badass when she met the ML. She was one of the first women ever to be accepted into law school, which is where she met her husband, an icy Marquis-to-be. She fell in love, hard, and forgot herself for a long time as she put aside her childhood ambitions of becoming a kickass lawyer for justice for her husband's sake and to be a traditional wife. She was happy enough for a while, but her frigid husband smothers most of the affection out of her over the early years of their marriage by his lack of appreciation, attention, and care. It's a love killed by a death of a thousand papercuts. She describes it as each offense adding another log onto the growing pile in her chest.
The final death blow to her love for him which sets the entire woodpile ablaze and then reduces it to ashes is that her sister dies, in a suspicious su*cide under odd circumstances, and he does not take her concerns seriously.
The FL files for divorce, sneaks out to her freedom, and plans to join the local police force so she can investigate things herself.
On the ML's side, he is shark like and calculating. He has childhood trauma preventing him from believing in love and preferring the security of the status quo where he receives all of her endless love and never has to return it.
Spoiler
He was in a carriage accident as a child which resulted in the deaths of both parents. The accident was much romanticized, and it is commonly held that his much-in-love, 'ideal couple' parents died tragically and beautifully protecting each other and their son. While we have not gotten to the details yet, I have the feeling the reality was much uglier, such as his mom tried to ditch him to save herself, and/ or the dad doing the same to save his own skin as well.
He does (secretly, wayyyy deep down) love the FL, (he broke convention to marry FL, a commoner, and the majority of his work and effort is so that no one will ever look down on her,) but he does not allow himself to even acknowledge it to himself. There is something childish about his requirement that he get unconditional love while being a selfish butt, like he wants a mommy, not a wife, even as he ignores her to do his own thing.
Anyways, his wife leaving triggers that shark-like possessive streak of his, so if you like that smidge of yandere, this'll appeal to you.
The success of this ambitious story will depend on 1) how well the mu*der-mystery is pulled off, 2) how convincingly they can navigate back from a Walkaway Wife Syndrome situation, which is next to impossible to do in real life, and 3) the personal evolution of the characters, which will need to be complex to make sense. The FL needs to re-find herself and become the professional shark she was all along to match her workaholic husband and actually speak up when he doesn't meet her needs and hurts her. The ML needs to get over his childhood trauma, realize and express his feelings, embrace the Power of LoveTM, and be a better, more demonstrative husband, while ditching the weird, proprietary, mom-and-kid dynamic he set up with his wife.
All 3 of those things are a tall order for any author. If it can be pulled off without shortcuts or plot magic, this'll be one of the truly great stories on here. If it can't, it'll just be average to meh garbage.
It's still in its earliest days, so I don't know which way it will go, but here's fingers crossed hope that it turns out amazing.