If you have a lover and that lover breaks up with you and goes off with someone else, that’s a breakup and a heartache and something to get over. If the person your ex-lover goes off with is of a different gender than yours, is this in some way a greater betrayal than going off with another person who shares your gender? Or is it less so?
Does it make the personal breakup into something greater? Is it tempting then to say that the pain of losing a lover is more piercing if the person is also repudiating a lifestyle or a society by crossing a gender line? Does it make the breakup easier by subsuming the purely personal and faintly mundane heartbreak and loss of the breakup into the righteous anger of the betrayed group identity?
I’m a tad confused by the animus against LUGs expressed by some hardcore style lesbians–it seems to me that having a bunch of hot to trot chicks to rub up against is no bad thing, and whoever figures every single hookup will lead to a committed love relationship anyway? So what if she goes off with a guy after you, would it be any less painful a breakup if she took up with your best friend? I’d think losing your lover to the penis side would be less painful–it’s not that she found someone like you but better, she just wanted to go in a completely different direction, and that’s less a slap in the face in my book, anyway.
I just think women are less likely to be absolutists than men. I’m one of those darned fence sitting bisexual types myself, and for me it’s usually all about the person–if I want to have sex with someone I’m not too picky about what genitalia they have, is all. I didn’t realize that I HAD to get my toaster oven before I was allowed to enjoy a roast beef sandwich with sprouts…
Hmm, on rereading it seems I have about as much point as the OP had a declared debate, but these are some questions I’ve been mulling over for a while… Pardon the hijack, if such it is!

Yeah, we were prats too, no doubt about it but still, when did the labels become so important? I think that was one thing we had right back then, and I’ve never had any reason to change my mind on this front. Labels suck, they limit people in the worst way–by causing them to censor themselves. “Oh, no, I can’t have sex with this girl who gets my motor going, because I’m a GAY MAN.” “I can’t be attracted to that guy, I am a STRAIGHT MAN.” “Mustn’t fantasize about penises (or in some circles even make use of penis shaped toys) because I’m a LESBIAN.” LUGs are just saying “Hey, right now I’m sleeping with her, then maybe a him or two, a couple more hers, who knows what I’ll be in the mood for next?” and that seems to be more essentially honest than the Procrustean self editing necessary to pigeonhole the gamut of polymorphous perversity humans are capable of into a “lifestyle.”