Agree and disagree, Smurf.
Not good to generalise that "lesbians" are biphobic.
On the other hand, if it's your experience that your mates dumped you or the only gay disco in town wouldn't let you in, you could be forgiven for your negative feelings.
Most bi women are really quick to qualify their rants about lesbian biphobia, which almost often erupt in reaction to a good example of it.
Regarding friends, I feel uncomfortable with your inference that if our friends dump us after we acquire boyfriends we are obviously cr*p at chosing friends. Most of my friends were fine, but I lost one (temporarily) and it was a horrendous loss. I lost more friends (tho only a few) when I came out lesbian, which isn't surprising because I was much younger and the resilience of our relationships were relatively untested by big life events. It can be hard to make friends; it doesn't come naturally to everyone. We make friendships within complex social frameworks (where you live, where you work, where you socialise, how much money you have, whether you have kids, whther you drive, whether you have a disability etc etc etc) - some people don't have a huge amount of choice but it doesn't been their friends don't mean a lot to them.