I helped my Stepsister Choose Underwear for the First Date

My 18 year old stepsister was getting ready for her first date and wanted help choosing clothes and underwear. After the first sexy lingerie, I got horny and started masturbating discreetly. After a while she caught me and wanted advice about sex, I couldn't hold back I fucked her doggystyle, then cowgirl rode me and we went into missionary position. Finally I cum huge load in her full mouth.