Surely a woman passing through a ‘phase’ where she is in an exclusive intimate relationship with another woman would classify as a lesbian?
The term bisexual to me implies someone who is shuttling back and forth between men and women for fun.
This is certainly my experience in dating women who classified as bisexual. We simply had a string of dates and lots of sex. I had no expectations that these encounters would lead to anything more. Interestingly none of them wanted to be referred to as a lesbian or ever come out as one. I suppose bisexual seems more socially acceptable and one can be forgiven for an error of judgement. Or two. Or three. Or four…
I think the problem with bisexuality that you are describing comes from the fact that for some it describes a bi-sexual and bi-romantic orientation whilst for others it describes purely their sexual orientation, the bisexuals who are 'problematic' for the gay community are the ones who are mostly hetero-romantic, but not all 'bees' are like that.
'Lesbian' or 'Gay' as opposed to 'homosexual' describes more a psychosexual
orientation, but 'bisexual' for some describes only sexual behaviour, whilst for others their psychosexual orientation.
Basically I think 'bisexual' just stopped having a descriptive meaning, I'd much rather see it reserved only for the case of bi-romantic + bisexual people: who can and want to have a romantic and sexual relationship with either a man or a woman and they don't care which one. OR find a different word for that orientation similar to 'lesbian' or 'gay'.
People who are sexually attracted to both genders but romantically only to one, are technically hetero-romantic bisexuals or homo-romantic bisexuals.
People who are attracted to both genders romantically, but sexually only to one, are bi-romantic homosexuals, or bi-romantic heterosexuals.
All of this are horrible mouthfuls to say, personally I think I fall into the bi-romantic homosexual category: whilst I can have physical sex with a guy, something always is missing, period.
I think because today we identify orientation as 'attraction' and many bi-romantic, or bi-sexual lesbians are attracted to men on some level, this makes them adopt the 'bi' label, because attraction=orientation, when I don't think it is as simple, I think there is some innate part of us that makes us either more compatible with women or men and desire romanic and sexual relationships with them. This problem would not exist if we allowed for attraction to just exist as a thing in itself, without it having to define our orientation, and if we defined orientation as a innate trait of psychosexual compatibility with one gender or both.
The problem really stems from the fact of how narrowly heterosexuality is defined, if you step outside of it, you are automatically non-straight, when really a person who is bi on only one aspect of their psychosexuality, really still fits more or less into the 'straight' category, because their long-term relationships will be straight.
This narrowness found its way into the queer world as well: you are attracted to the opposite sex in some way= you are bi, when this often is not the case.
I guess keeping the 'bi' label by people who live predominantly gay or straight lives has to do with keeping personal integrity, to 'owning' their past.
It makes sense, but only for people who are bi in the psychosexual sense, for ones who innately don't have a gender preference in terms of forming relationships.
Personally I am not bi in the psychosexual sense, I am bi-romantic and gay, and in my case I've felt that I was pressured into the 'bi' label by a world that demands from us to justify our attractions and want to define us by them.