Beth is looking for a dress she told your girlfriend she could have, while she is on her hands and knees though you notice that her dress has risen up so much that u can see her ass and thong. When Beth goes to pull it down she realises just how much is on show, she turns around to see the massive bulge in your trousers and clearly gets excited. Beth tells you that as long as you only touch yourself technically u aren’t cheating, she then sits on the bed to show you her panties and pussy.