These walls are paper-thin, and I'm tired of hearing you getting rejected by your wife every night. So what if she's my sister? She's a prude and you deserve pleasure! So just keep quiet and I'll take care of you myself. Don't make a sound, don't move too much, your wife could wake up at any moment. Shhh Just let me stroke you and edge you, whispering dirty things to you while building up a nice big orgasm. Be a good boy and don't cum until I say so, or I'll have to punish you. Just lie back (quietly!) and let your sister-in-law milk you the way you deserve.