Why am I always everyone's big brother and nothing more?

every time I have a new romance with someone I already know I'm already their big brother and they have not interest in me for a relationship. but they wanna call me up and ask me for help while they are in theirs because they value my opinion. why is this. ill give an example this one girl I've dated her before well her and I have kept in contact for years and would get to almost dating then stop talking then do that again. well this last time her and I were flirting constantly always txting always talking and having fun. when I was with her she was all over me even sitting in my lap and kissed me when I left. then all of a sudden next thing I know she stops talking to me and I work hard talk to her again then she tells me that she only views me as a big brother. and not romantically. the girls I have been with I have pleased to no extent. one girl I did a FWB asked me how I don't have 10 girls eating at my palm right then. I just want to know why I can't even find one to date that doesn't view me as a brother and wants a relationship with me.
Why am I always everyone's big brother and nothing more?
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