I found this post about ‘for beginners’ quite interesting. I could see a learning curve being explored and that would have to be approached in a particular way i.e. building a palate. I would start with some of the short stories of M. T. Vasudevan Nair. The way he conveys repressed emotion and unspoken tension in his stories is masterful. ‘Vanaprastham’ (the story and not the film) is a great example of a quiet, aching sort of sensuality which would allow the beginner to experience and learn to appreciate subtext before graduating to more obvious narratives.
I wouldn't trust any app that promises this exact combination. I suspect most such apps are looking to extract value (or information) from you and will deluge you with a barrage of ads. It’s far safer to go with large, established platforms that do have Malayalam audio and let you browse through for more mature romance stories. Yes, you might have to trawl through more stuff but it’s far safer, far more ethical and will give you a far better user experience in the long run. Kuku FM and Spotify are traded on the stock market or are large companies with reputations to uphold. A small app called ‘Malayalam Hot Stories Audio’ has no such reputation.
Use your secondary email address to sign up for any service online and avoid linking social media profiles. Be extremely cautious when a service asks for permissions to access data, etc. It is highly likely that the best audio content for mature romance stories in Malayalam are on the following services: Kuku FM and Spotify. They have a large audience and professional creators to serve that audience. Shady standalone service that seems too perfect to serve your niche, sensitive desires online are best avoided.
For more information on the culture surrounding such content, one might find such images and other content mentioned in forum posts about specific cartoons in the appropriate sub-forum of a particular anime or cartoon forum. While the bulk of the post would be admissible as relevant as it would discuss character relations, there could be a point in the post where someone links to or otherwise mentions a ‘kambi’ (erotic) comic for that series that somehow attempts to stay ‘in-character’ for the story while exploring same themes that the series itself has caused the fandom to debate about (e.g. who would make good couples, what character’s true motivations are for actions in the series). Thematically, such comics explore same themes, but are taken to an explicit conclusion. Note that such ‘kambi’ comics are found on the fringes of the fandom, but are a persistent part of it.