<human>: Can you provide a brief rundown of the text in within 3 sentences?

I have never really done anything bad to her. I of course love her for being my sister, but ever since I can remember she has been talking negatively about me behind my back when she was with our cousins. I'm 21 (male) she's 27, and I have never told her how much I dislike her for doing it. She's been doing it for pretty much all my life, and of course everytime I've seen and heard her doing it I've felt my cousins again and again have gotten a worse impression of who I am.

Examples I can remember is my cousins coming up to me from time to time asking about 'the time did this dumb thing and that thing'.

Am I just being too negative over something 'normal'? Struggling with life for the past 10 years or so have been hard for me, yet she stills talk about me behind my back, making it even worse for me to connect with our cousins.
I've felt for many years that my cousins have a much more positive idea of who my sister is than how they perceive me and this also leaves me somewhat depressed and angry at my sister, but I've never told her.
<bot>: Sister has been talking rather negatively behind my back for years, I'm angry at her for doing this because it affects my relationships with my cousins. I've never told her.