Forgetting all my intentions of finding out my stepsister’s secret lover, then, I bump into her homosexual affair through a sensual scene

I remembered once, I opened the door without knocking and found my stepsister fondling another girl, the latter had a big behind that was being pounded by her eagerly. Taken aback yet sexually stimulated I complied and ended up with a crazy threesome along with the revelation of a taboo family secret.