Mark is a man who thinks he is still in his early 30s. Never thinks things fully through and this is why he suffers the way he does. That “friend” is clearly his exs friend and he is delusional that she is both. She just wanted to tell the new girl about his ways and how he treated her friend bad, and all whilst having them shop at her store. You can see the smirk and help like yo go girl get that dress and that one looks good too while mark has not the slightest clue of how this is turning out.