Honestly, if this was me and my boyfriend I'd be really pissed. If my being bi 'changed everything' for him, then I'd probably be outta there. I'll never understand why some people are so insistent that being bi = greedy, or a cheat. If she's with you, she's with you. You're straight, you like girls. That doesn't mean you like every girl and that you're a cheat or whatever. She likes girls and guys. It doesn't mean she likes all girls and all guys. She's with you. She likes you. She probably isn't looking for anything else, and if she is it isn't because of her sexuality. Her being bi doesn't change a thing.