I'm 24, I'm a giant lesbian, and I was raised in a very religious family.
It's okay to watch pornography and to fantasize. I know it's difficult to overcome the idea that it's wrong and shameful, but it isn't. Just remember that you haven't done anything to hurt anyone. You haven't done anything to your friend. She can't read your mind, so she isn't going to know about your fantasies unless you tell her about them.
I can't tell you if you're a lesbian or if you're bisexual. Only you can figure that out. It's okay to be uncertain about your sexuality. Sexual identity is very complicated, and it's okay if it takes a long time for you to understand how you're feeling and what that means to you.
When I realized that I was a lesbian, the only way I was able to stop feeling guilty was by accepting it. That took a long time, and it wasn't easy.
I wish I had good advise for dealing with the anti-gay laws in Nigeria (if that's where you're still located). I really hope someone else here will be able to help you with that!