If Emily fancied Jack that much over the Euros, she'd be looking him up and would've seen the articles about his 'secret' gf Sasha. I don't believe for a second that she thought he was single if the rumours are true. She should say with her whole chest that she knowingly shagged a man with a gf. Jack can't even deny that they're 'on' at the moment because Sasha regularly uploads evidence of her in his house. Jack is a serial cheat and Sasha should've left him a long time ago, we know that, but Emily is proper vile for consensually putting herself in that situation too.
Also I wonder if Sasha pays her way in the relationship. Jack is on so so much money - I wonder if she offers to pay for any of the bills and he lets her or if everything just goes on his card. Must be hard to leave someone who pays for the most luxurious roof over your head and everything else, even if they are a big fat cheat. She always seems to be doing BooHoo shoots so she'd be able to afford a nice apartment and her M&S goodies but she wouldn't be able to buy whatever she wants without looking at the price tag like she probably does now.