I think Dev knew he had a bird in the hand (Karen) and Archie was his alternate and giving him something he wasn't getting from Karen ... even if it was only time.
Why would Archie show up at Dev's apartment and then kiss him without some encouragement to do so? Dev is/has been definitely keeping Karen while he tries out some new stuff. Dev is definitely a dog and Critical was spot on about his pick of Ivy.
Julia, on the other hand was trying to balance the show and the adoption possibilities, etc. It is obvious that she loves her husband and son and they love her. Michael was some window of escape. She seemed to really love him in a way.
So, if we are going to talk about double standards ... why if we are more forgiving (in general) of philandering husbands and boyfriends why not forgive a straying wife? It appears her family has.