I like this boy but? PLEASE ANSWER?

by the way I'm asking this for the 2nd time just because I need more answers so yeah.
Ok so i like my sister's boyfriend's family friend's son. I only saw him once in real life but we followed each other on Insta after that. And he likes my pictures and is aware of my age. Anyways my sister's boyfriend doesn't want us together and I heard from my sister that he talked to my crush about how I'm much younger than him , I'm still a high schooler , and told him not to text me. He did the same to me. And my crush is only 3 years older than me! Actually literally 3 years older than me because our birthdays are in the same week lol anyways. So yeah I like him so much but he won't text me because of my sister's boyfriend !!! What should I do please please someone help ! : ( in January I will turn 17 when he turns 20.
I like this boy but? PLEASE ANSWER?
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