The Granddaddy of BL
Visual depictions of homosexual intercourse is not something new in Japan, as these shunga (erotic art) show. From what I know, these pieces are from 18th-19th century. All images are from Wikicommons, as usual.
(And one piece of love between the ladies, just because I can.)
For a short but educational read on homosexuality in shunga, check out this article.