There are several dedicated BL manga websites. For example, Mangago and Kissmanga have a decent selection. But be careful as some of these sites might not be legal or safe.
You can try some websites like MangaFox or MangaReader, but be aware that not all of them are legal and may have issues with content quality and security.
There are a few options. ComiXology has a decent collection. Also, Webtoons sometimes has manga available. Just make sure to check the licensing and legality.
Some manga publishers offer free chapters or limited-time promotions on their official websites. Keep an eye on those. Also, there are a few apps that have partnerships with publishers to provide free reading options within certain limits.