Rin is 100% to blame here and I have no idea how people think Momoka is the problem.
The circumstance at the start is that Momoka dates and flirts with a lot of people.
Then Rin has a problem with those circumstances and wants to change them
Then Momoka tells her directly what actions Rin would need to do if she wants those circumstances to change.
Then Rin agrees with those actions.
Then Rin realizes she has issues with those actions and imposes additional rules on Momoka.
Then Momoka agrees with those additional rules as long as Rin keeps up her part of the deal.
Then Rin breaks her deal yet again.
Then Momoka gets understandably pissed and tells her not to contact her again.
And now you want to tell me that Momoka is to blame somehow?
I mean of course both of these girls have massive issues and both need a therapist in an ideal world, but morally, Momoka's only offence was getting jealous over Rin, while Rin has imposed her values on Momoka, then refuses to uphold her obligations and takes her for granted and leads her on.
Anyways, interested where this is headed