I don't know how many people have read John Varley's Gaea trilogy (it's a strange mix of fantasy and sci-fi but I love it for that) but the main characters are two women who end up being in a relationship. Both of them have been with men in the past, and while one of them, Rocky, continues having relationships with both men and women, the other, Gaby, remains faithful to Rocky. There is also an entire community of women who breed by themselves; one of its members ends up with a man, much to her mother's dismay, but I don't think this affects the community much. (Her newly found bisexuality, while genuine, is portrayed as an act of youthful rebellion.) I can't think of male characters having a homosexual or bisexual relationship - I last read these books some years ago - but I wouldn't assume there aren't any.

The Bechdel test passes with flying colours, seeing that, like I said, the main characters are women, there are many major female characters, and they all have lives and missions and whatnot. Where I need to put a caveat is that I'm straight and therefore likely oblivious to stereotypes and nuances that lesbian and bisexual readers might pick up [SPOILER: One of the main couple dies, causing much angst for both the other and the reader, but is later revealed to have been transformed into a more powerful being, and they both remain together and pretty much superhuman.].

For what my opinion is worth, I thought Rocky and Gaby were an ass-kicking pairing, and remain one of my OTPs.