One great free lesbian short story is 'A Safe Girl to Love' by Casey Plett. It beautifully explores the experiences and emotions of lesbian characters in a very relatable way.
Another option is to check out some LGBTQ+ literary magazines that sometimes publish free short stories online. They might have some excellent pieces that focus on lesbian relationships, such as stories that deal with the cultural and social aspects of being a lesbian, like family acceptance or the lesbian community's unique bond.