Films similar to the first half of In Secret

There's plenty of period dramas that could fit the bill. Jane Eyre, North & South, Jude the Obscure, Far from the Madding Crowd, The Buccaneers, Desperate Romantics. Hope that helps.

Anna Karenina and Madame Bovary are classic examples. For the romance novel version, there are the films made from Barbara Cartland books.

The painted veil

Lady Chatterly's lover by DH Lawrence.
I like the British tv series version 1993 With Sean Bean. You can find on YT.

Lady Chatterly is feeling thoroughly unfulfilled and bored and married to a disabled husband who's not very attentive and also feels inadequate.
She has her eye on the game keeper. He's a rough but rugged kind of man She is attracted to him. And they have this animalistic kind of chemistry.
There are different versions of this story made into tv and film.
I haven't checked them all out.

Also the British BBC Tv series 1970 version of Thérèse Raquin is brilliant and my favorite version.
Some kind soul has uploaded it onto YouTube and it's in three parts.
I would recommend watching This version.

I'm partial to the British dramas as I'm originally from there but these older series are just so well done and are still enjoyable even today.