I'm not sure what's going on in Rin's mind. She needs to make up her own, either dedicate herself in the relationship or just don't care about it.
I get that to her, this was superficial and a way to gatekeep Momoka and suppress her 'trauma' (about her mom). But that doesn't mean her intent can't be made clear to Momoka. They both should sit down and have a real talk.
(I'm genuinely enjoying the manga, I don't dislike any of the 2 main girls either. I think it's very interesting and I hardly turn away from one, unless it's really bad towards the end.)