First my dear you need to pause.
Emotions are healthy-they help us define our own limitations.
However-how we act upon them is sadly often not healthy.
NO person should be in a relationship that leaves them feeling good BECAUSE the other person wants/needs them. We all need to be completed and happy within ourselves before we can have a healthy relationship.
That doesn't mean all people can handle their significant other having another.
BUT-it means you are already dealing with unhealthy behaviors in yourself-and you can't possibly address issues with her until you get a handle on those.
The bottom line is if she is Bi-which is my guess if she has you and wants a woman to (unless you are a woman and I missed that in my reading) you CAN NOT fulfil all of her needs nor can a woman. NEITHER of you can. Period.
Doesn't matter HOW wonderful either of you is.
As a married bi-woman I know this first hand. I ADORE my husband. Love of my life, great guy and wouldn't ever want to lose him. But he can NEVER be my everything. It's impossible.
Good luck. I have to run. I'll write more if it comes to me later!
"Love As Thou Wilt"