"Touching my penis calms down..." My older sister, who has calmed down when I touched my crotch since I was a child, still touches me when I feel uneasy even now as an adult. I refused...

My older sister, who has calmed down when I touched my crotch since I was a child, still touches me when I feel uneasy even now as an adult. If you touch your dick so much, you'll get an erection! The older sister says, "Don't make it big," but doesn't stop touching her. One day, I said, "You're all unfair, sister. Please show me to me," and she shyly showed me naked and let me touch her. I get so excited by the naked body that I saw for the first time that my sister was naked and I get a full erection! Furthermore, her sister got excited and forced to cum three times in a row in a cowgirl position! !