Ok this is where I have some issues with labels.
It doesn't matter if your gay ,straight, no, poly, pan or ace.
You should be treating your partners with the same respect and affection you want to receive yourself.

I don't think she is confused about her sexuality, imho she likes the label. I think she knows exactly what she wants, which is a main course with desert on the side but without paying for the cheque.

She has two people massaging her ego with no reason to stop. You have seen for yourself how capable she is of using her current boyfriend yet you feel you would have better luck?

So here is the question, why do you feel your only worth someone like this?
She has no complications or regrets about sleeping with someone whilst with someone. Permission or not, most people feel uncomfortable with this arrangement.

You are aware she has a lovely boyfriend who she is essentially using because she knows she has it made.

What is it about this girl that is so attrActive, because it isn't her treatment of others?

On a hypothetical note, supposing you got together, and she comes to you saying There was a guy she was really attracted to. That she just wanted a fling, but it meant nothing?
I ask this cos I hear it alot in bi/gay relationships.

Perhaps you should look at why you form these attachments so quickly, what it is your really looking for and is this person honestly the right person to provide you with what you need?

I hope that whatever hAppens everything works out for the best and you find someone who is happiest with just you.