I'm a high school virgin, deeply insecure about my inexperience. I'd never even held someone's hand, let alone kissed anyone. Every day, I practiced kissing alone, but nothing improved. One day, I tried confessing to a classmate who I'd heard liked me, but sadly, I got rejected. After that, I fell into despair, convinced I'd remain a virgin forever. Around that time, my older sister returned to our family home after her husband's infidelity. Now a married woman, she carried a sultry, erotic aura. When I told her about my rejection, she laughed mockingly and insisted on letting me practice kissing with her. After persistent begging, she reluctantly agreed to let me practice through a glass cup. Watching her tongue writhing through the glass drove me wild with arousal. Unable to bear the barrier any longer, I forcefully tried to kiss her directly. At first, she resisted, but once our tongues intertwined, her body began burning with desire. Later, she admitted she'd been sexually inactive for a while. When I pulled down my pants and revealed my erect cock, she hesitated but began sucking it with apparent pleasure. She swallowed my cum, her expression transforming into that of a satisfied woman. From then on, she willingly let me touch her body. One day, a letter arrived from her husband, saying he'd gotten another woman pregnant and wanted a divorce. Seeing my sister cry, I couldn't hold back—I embraced her and finally crossed the forbidden line.