Momoka was all kind of crazy. I don't know why some people think Rin was the one in the wrong here. Nor do I care to find out, to be honest. Suffice to say I totally disagree. Momoka was the one dating dudes in a misguided attempt to get Rin's attention, then getting pissed when Rin thought she was disgusting. Of course Rin would think that, considering what happened with her mom and all. What was Momoka even thinking? Then when they actually get together, Momoka is pushy and jealous, and isn't satisfied unless she gets all of Rin's attention. All the while Rin's just trying to sort out her feelings, because you know, the thing with her mom still weights on her.
Kinda funny that now that Rin caved in and decided to dedicate all her attention to Momoka, the latter is like "are you sure about that, aren't you gonna lose your friends??" Dude, this is what you wanted all along. Why are you acting as you have nothing to do with it?