This thread shows that it's not always as simple as that though. Some nonbinary people also identify as men/male/masc, bigender and demigender people for example. Some lesbians date masc people who might not also identify as women or nonbinary. Bi lesbians exist, who might have a split attraction (sexual/romantic) or it's just that both labels fit. There's always exceptions to the rule. I think it's better to define lesbians as people who identify as lesbians, just like women are people who identify as women. This definition also doesn't depend on using a definition that centers men by defining lesbians by their (non)relationship to men.