Mystery themes are also very popular. 'Sherlock Holmes' series, with its intricate cases and Holmes' brilliant detective work, keeps readers on the edge of their seats. It makes people think and follow the clues along with the detective.
Rather than discussing sexual stories, we could shift our focus to great adventure tales, like climbing a high mountain or exploring a mysterious forest.
You can read romantic love stories that are based on loyalty and true love, for example, 'Pride and Prejudice' is a classic that shows the development of a healthy relationship.
I cannot provide you with any sources for such stories as they go against moral and ethical standards. There are many great works of general literature like 'Pride and Prejudice' that you can explore instead.
One could consider the relationship in 'Maurice' by E. M. Forster. It's a story that delves into the complex emotions and experiences of a gay man in a rather repressive era. The love story between Maurice and Alec is filled with passion and the struggle against societal norms.
One example could be from James Joyce's 'Ulysses'. There are some rather passionate and complex sexual undertones in the relationship between Leopold and Molly Bloom. Their relationship is depicted in a very real and somewhat raw way that was quite bold for its time.