Is it okay to feel this way for my best friend?is it normal?

m single.hes my bestest friend in the whole wide world.i love him to death.i cant imagine life without him and he is my most favorite person in the world.im ferociously possessive about him.im 17.hes 23.we met randomly on a networking website,3 years back.im an only child and iv always longed for an older brother and iv looked at him as an elder brother since about a year now.i luv it when he calls me his little sis an little devil.we talk everyday for atleast 2 hours and i even alter plans to make sure that i get to talk to him everyday.he has a girlfriend whos like an angel and i completely adore them together!the twist in the tale is i thought i was infatuated to him 3 years back.is it that im yet not over him and im not realizing or is it that i was just small and naive back then?is it normal to love a person sooo much in a platonic way(when i try to think what it is and i wonder if id like to hold his hand or kiss him the answer is definately NO so i guess it is platonic atleast as of now) or is there something im missing out on in this whole situation.how can i be in love with as people say and also feel happy when he calls me his lil sister?