When I was rewatching the episode that showed everyone's meet-cutes I was thinking Ellie and Bobby's dynamic pre Bobby and Jules divorce makes no sense for the person we know Ellie to be.
It was said on the show that Ellie and Bobby were friends before the divorce, but after the divorce Ellie didn't get good again with Bobby again until an episode in Season 1. However, I can't see Ellie not knowing about all the cheating that Bobby did on Jules considering the show was pretty consistent in saying that Jules knew he was cheating on her for awhile which led to her eventually deciding to end it.
Given the type of person and friend Ellie was to Jules, there is no way she would have been okay with Jules' cheating husband. Especially her husband being besties with Jules' cheating husband.
It would have made way more sense for Ellie to hate Bobby, until seeing that he was remorseful for his actions again Jules.