My girlfriend is bisexual and has feelings for another girl?

long story…but I need help. I would appreciate it if you could read this all, if its not too much to ask. thanks…

So my girlfriend is bisexual…we often have little fights about it. not because im opposed to it, its fine with me if thats how she is. but what im not ok with is if she has a relationship with somebody else while she’s with me, I dont care what gender they are, my feelings are still in her hands. we have been together for about 2 and a half years now, and I love her with all my heart. and she loves me. I hope. Today she told me she had feelings for somebody else…and its a girl. she never gave me a chance to reply, because after that she said she had to go, and never said a thing after that. so now im sitting here, more hurt than I have ever been in my whole life. shes spent the past 2 years telling me she loves me, im her only love. that shes all mine, and im all hers. im the only one she’ll love. and now shes telling me she likes this girl? how in the world can she possibly love me the same way she did before? I would never, ever, ever, in a million years, even think about having feelings for somebody else. I can honestly say that in the 2 plus years we’ve neem together, I’ve never thought about being with another person, not once. how am I supposed to feel? im sitting here, trying to deal with it, nobody to talk to, and its just there. theres nothing I can do. I cant change the way she feels. and im scared that if I tell her about how I feel that shes just going to feel bad and say she wont like the girl anymore, which is a lie, she has feelings for her, she cant change that.

just how can she do this to me? tell me she loves me, tell me im her only one. and she likes somebody else? im so hurt, I feel so unloved, so unwanted. so unneeded. and really alone. I dont know what im asking from you, just if you can help in any way. please, I need it.

and so you know, our fights about her being bisexual are usually about cheating. she thinks it wouldnt be cheating, since its with another girl. I do think it is, because my feelings are still involved. I love her. to know she has feelings for somebody else hurts me really bad.

I dont want to end this, I love her too much. but everytime I look at her im jsut going to feel this hurt inside. knowing that she doesnt feel the same way I do…nothing can be the same anymore, and that scares me.

help?