My sister is better than me in every way, what should I do?

Anonymous
I have a sister who is prettier, thinner, and wittier. I have ADHD and mental health issues, whicj she doesn't struggle with. Objectively I know I am just as intelligent as her, we have very similar IQs, but my friend keeps calling me the stupid sister, and when I make a comment refers to me as such. He calls her the better sister, and I'm afraid my other friends agree. I have low self esteem and this doesn't help. I can't stop being friends with this guy as we are in the same friend group at uni.
Updates
+1 y
Just to clarify, the others in my friend group think he's being a dick.
My sister is better than me in every way, what should I do?
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