Navigating free erotica ethically is trickier than general fiction, but possible. I'd steer clear of random download buttons; those sites often bundle malware. Legally, the 'free' usually comes with a catch like an author's newsletter sign-up or a temporary promotion.
Project Gutenberg has some classic, older works that are now public domain, but the selection for modern tastes is limited. My preferred route is checking authors directly. Many, especially in indie romance, offer a free short or first-in-series book on their websites or through major retailers like Amazon or Kobo to hook readers. That's the safest legal download—straight from the source with the author's consent. The quality and themes are more reliable too, compared to some aggregated sites where you don't know what you're getting.
I've found a few favorites just by signing up for newsletters from writers whose blurbs I liked. It does clutter the inbox, but you can always unsubscribe after grabbing the book.