Ross’s arc is learning to trust again, and the copy girl was a big part of that.

When the show begins, he’s recently divorced from his wife, the mother of his child, who has not only been cheating on him, but hiding a huge part of who she was. It’s played for laughs, but Ross has massive insecurity issues throughout the show, repeatedly putting women on pedestals and engaging in absurd displays of jealousy and peacocking.

Rachel was the ultimate prize, the one he’s always wanted, and getting her turned out to be an actual relationship with all of its ups and downs. He was beginning to see Rachel as a person instead of aome external validation that he’s a worthwhile man and partner. Taking a “break” massively undercut his ability to manage his insecurities, so when copy girl flirted with him, it was like an awakening. He wanted her, he was unattached, and she wanted him. He knew it would upset Rachel, but he was angry and hurt and didn’t care about her feelings in that moment.

His arc finally landed when he fell asleep reading her letter and unknowingly took full responsibility for their issues as a couple. Old Ross, recently divorced Ross, might have bit his tongue and taken the abuse because he felt inadequate, unworthy of Rachel. Post copy girl Ross realized that he is good enough as he is, flaws and all.

He knows he hurt Rachel, and he regrets his decisions, but he sticks up for himself and insists she accept her share of the blame. He wants a relationship, but one built on trust and mutual respect. Rachel is off the pedestal, and it takes a while for them to come back around (I honestly don’t remember the timeline for later seasons).

One day after breakup you will have some lingering feelings and hooking up with someone else just to suppress them is not a healthy reflex I think. Especially if the other person doesnt know youre with them just to strike a “hit” and feel less shitty with yourself.