Bonnie is your girlfriend's sister but you can't help but get a good look at her tits when she looks through some of your paintings, she isn't wearing a bra and you have always fancied her so when you see a bit of nipple you get an instant erection. Bonnie doesn't take long to see it and realise what you're looking at, luckily for you she is more than happy to have some very naughty fun!