Am i selfish?

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there's a boy likes me from high school. even though he didn't say it out,alway says we're best friend, but i can feel that emotion. he is very good to me, always help me.every time i meet with something unhappy, the first person comes up to my mind is he. i can share everything with him. and i feel at ease being with him, without any disguise. although i know he's very good, and he have done many things to me. i don't love him. i like to be together with him, but don't want to be his girlfriend. today my best girlfriend told me that she finds she is getting to have a crush on him. and she knows the relationship between him and me. she said i don't love him, why not give him to her. i feel bad hearing this. i get used to his deep caring. i guess i'll be very sad to lose him when he has a girlfriend. i don't want to imagine she becomes his girlfriend, though she's my best friend. am i too selfish? feel so bad now.