What is going on with my best friend?

Were both girls, and I have never had such a close friend before. I feel so comfortable around her and we can talk about anything. We kiss on the lips... but i never really understood how it started. We just looked at each other one day and kissed. It felt so natural- and have been doing it ever since. When we have sleepovers, we always cuddle and hold each other. I never thought anything of it until she started holding my hand in public. I care about her so much and have unconditional love for her. But i don't know what this is, or what we are doing. I have been through so much with this girl and im not sure if were doing this because we have so much love and respect for one another... or if we have feelings for each other. I know I am straight. She keeps telling me that she wants a boyfriend and that if I was a guy then I'd be perfect for her. I don't understand Please help me figure this out.