So you're looking for those classic romance reads without dipping into your wallet, and you want to stay on the right side of the law. I get it. Mills & Boon is owned by Harlequin, a huge publisher, so they're understandably protective of their content. Legally, the main route is through library services. A lot of public libraries use digital lending apps like Libby or BorrowBox; you just need a valid library card to borrow ebooks and audiobooks. It's a fantastic system—you can place holds, read on your phone, and it all cycles back automatically. I discovered so many of their 'Medical Romance' line this way.
Sometimes, Harlequin themselves will run promotions on their website, offering a free first-in-series book or a sampler to hook you into a new line. It's worth signing up for their newsletter. Outside of that, I'd be wary of any site offering full, permanent downloads for free. Those tend to be pirate sites, and the reading experience is often riddled with pop-ups and weird formatting. Stick with the library apps; they're genuinely the most reliable legal source I've found for reading a lot without buying every single title.