Honest question...who felt sorry for Kristin when Tom and Ariana were having an affair behind her back?

So Tom is a cheater...that's obvious. But I always wondered why Ariana seemed to get a pass when she and Tom were carrying on while Tom was with Kristin and them both denying it all. "We're just best friends". Especially after she started working at SUR. Maybe my memory is fuzzy on the details but it seems like she herself was the other woman years before it happened to her. Am I not remembering that accurately?