That's why anyone in touch with reality knows that Lana's advice was pure crap; Sarah was the one in the wrong, and Jordan had no reason to feel even slightly apologetic for anything. Further, and there's no indication that Jordan and Sarah are not exclusive (hence all of the "you're the one for me" kind of plotting), so there's the natural assumption that they're in a stable relationship so it justified Jordan's equally natural reaction (initially, feelings of anger and betrayal). We will see if Lana is so cavalier about being the one in the position to accept "anything goes" relationships if her husband's affair becomes public information. Anything less than a consistent reaction is just another example of how Berlanti productions writes double standards for certain characters (e.g. on Supergirl[/], SG was all smiles and supportive of Kelly becoming the Gaurdian, but she was completely hostile to the idea of James taking on the role, threatening to stop him).