Maybe you like "pansexual" better?
Eh, you know, it isn't always necessary or helpful to tell parents everything we have going on in our lives, especially if they're going to be judgmental about it.
^ That was a similar thought that I had. When you're attracted to people despite gender, just for the person inside. That's why I always preferred to be called pansexual rather than bisexual.
But over all, the need to label it shouldn't be so great. People are constantly discovering and rediscovering their sexuality. I'm still exploring mine. You shouldn't have to define it or label it if you don't feel that it fits into a label.
My mom and me have a very close relationship, she knows I know adult film work and that I'm a professional dominatrix. But even still she doesn't know that I like women. When I dated women in the past she would always say 'I think it's just a phase you're going through, it'll pass'. Well now I haven't dated many women because I'm more nervous around them due to lack of experience (and my mom still thinks each woman was just a 'phase'), but I'm finding myself to me attracted to women and only women as of late, and that's what I'm looking for. How or when I will tell my family that, I don't know. I suppose only if the relationship gets to that serious level where I want 'family' to include them.
It's up to you to decide when it's really important for her to know. During these beginning stages it might be better for you to just keep it from her, especially if she's going to say statements like 'what did I do wrong?', which will just cause unnecessary guilt and stress for you.
If you do feel that she needs to know, or that you can't keep it from her the situation might be difficult to explain. Many people don't understand polyamory and many don't agree with it.
I don't know how I would go about explaining polyamory to my mother.
She doesn't sound like the type that's going to be very supportive about your choices right now, so I would say don't worry about telling her for now. Let her think it was just some phase, or that it's over. Then enjoy the time you're having with this new woman in your life. Without being made to feel guilty just because your mother doesn't understand it.
Just my thoughts. Hopefully something you read here in this thread has helped your situation. Just remember to have fun- and don't worry too much about the negative people in your life, because then you could end up spoiling it.
Focus on the present and just enjoy it