It could be that you're bisexual, and that you're fixating on these women because you're bored with your boyfriend.
But, you could be a lesbian. It depends. Are you becoming less and less attracted to HIM, or to men in general? Some girls do have crushes on men and later turn out to be lesbian. How do you feel when you're, y'know, intimate with your boyfriend? Whether or not you've had sex, how do you feel when you kiss him? And how old are you?
If you still get turned on by guys too, it could be that you've just got some sexual fluidity and that perhaps the reason you're going off your boyfriend is separate. If however you're liking girls more and realising you've never REALLY liked guys, could be a sign.
But please don't be in a rush to define yourself. As a bisexual woman I often hate the phrase, but for you, it MIGHT be just a phase. Whether or not you break up with your boyfriend, take some time to really think about who you are. If it's the occasional fantasy about women, don't worry, even my straight friends apparently have those. If you get feelings for women better and stronger and different to how you feel about men, however, you might need to take some time to reassess what you want.