Home    Stealing with my lover's sister

My girlfriend and I are not married yet, but we decided to live together for a while. She works in an office and I work as an engineer, so we both have quite stable incomes. One day her best friend Rin Natsuki came to my house and wanted to stay for a few days because her house had just been sold so she couldn't find a new place to live. My wife had also asked my opinion in advance, so it was quite normal for me for Rin to stay here. But her beauty caught my attention, that night I went in. In the bathroom, I saw Rin taking a shower. I peeked and smelled Rin's underwear. The next day my girlfriend went on a business trip, now Rin had something to say, she saw what happened to me yesterday and then I was scared and embarrassed. It was surprising when Rin turned to ask me for sex, how could I refuse?