Don't worry LP. You are perfectly normal. At your age it is absolutely normal to have feelings for both boys and girls. It does not necessarily make you a lesbian (although it is possible you are). Around this age and sometimes earlier, when your bodies hormones are changing, you can have feelings for anyone. There are a lot of straight females who like to watch lesbian porn even when they are much older but have no intention of having a relationship with someone of the same sex.
Many girls do explore their sexuality by having intimate times with other girls. There is nothing wrong with it. You can either continue to think of your BF when you masturbate or if you think she may feel the same way, tell her how you feel and see if she would like to be intimate with you.
When I was 13 I also had feelings for my best friend. One day when we were alone in my room, I got brave enough to tell her. It turned out that she had the same feelings so I kissed her and she kissed me back, We ended up naked on my bed touching and feeling each other. Over the next few weeks we did it more and more and became more adventurous and progressed to fingering each other and even licking each other. It was all a beautiful experience at the time.
As it turned out, we both ended up getting boyfriends and our sexual experiences with each other stopped. She was the only girl I ever did anything with but it was a great way to learn about our own bodies and what felt nice.
Another friend of mine had the same experiences with her BF. The BF ended up with a boyfriend but my friend realized that she preferred girls and was a lesbian. Either way it nothing to worry about. If you are too scared to tell your friend, then just enjoy thinking of her when you masturbate!!!!
Hope that helps! x
