Well, if you think you would be comfortable in an intimate relationship with guys as well as girls, then you may be bisexual. But if you feel comfortable with only girls, then you may be a lesbian. I don't think it matters who you have been with, but instead what's important is your feelings, if you have any attraction, and what you'd be comfortable with. It's up to you how you define your sexuality, since, you're the one who knows what it feels like best :)
Sometimes it takes a while to figure out what you want. For me, it's like this. If you can see yourself with a male the same way as with a female then that could mean you are bisexual, If you can only see yourself with females then you could be lesbian.
It's all about listening to yourself, your desires, your fantasies, your feelings. Try to leave out any other thought - what other people would think, what you're "supposed" to be according to people, what you always thought you were, what happened in the past... And focus entirely on yourself and what you want here and now. The answer is already there, you just need to allow yourself to see it! And it seems to hard for you to do, just go on living your life and following your feelings and desires, and they'll lead you to your answer. After all, you can take all the time you can, you're not obliged to label yourself until you're totally sure!