Should i just leave him for this?

I still cant get over the fact that my husband is infaturated and into my big sister. I have 4 big sisters, im the youngest one, and he NEVERS talk to any of them, except the one before me. He gives them all the cold shoulder, respond in a monotone, and never looks at them. But when it comes to that sister, hes so happy, all smiling, talks to her, says hi, and bye in a high pitch, happy voice, always looking at her, smiling. Eck, it just makes me look at him different now, at the same time, hurt. He does this to her because shes my sister, and he doesnt think i wouldnt notice, but i SURE AS HELL DO! Ive talked to him about it, and he just got angry and acted like im being dramatic.