Yeah, I get that. It's just it seemed a little forced. Like, the detail of the threesomes before being revealed of a cheating situation added nothing to the fact that he cheated on her. The backstory should've been just that, he cheated on her.
I found adding details out of the blue, like Ivy saying "oh yeah, we made out all the time" or "we did this all the time" and the whole "yeah, I had a bunch of threesomes with him", doesn't really expand on the character. If there was a need to show Lena was interested in those types of stuff, there could've been another context without just saying she had already done it. Like telling Holly or Ian or Ivy "I'm actually interested in trying things with other girls".
It seems the only reason the whole Cherry threesome thing was added was to give a justification why Lena won't accept a threesome or other type of situation in the future, because the thing that made her hate Axel was the fact he was already fucking Cherry before the threesome (exactly Ian's situation).