Aye, Eripiyo's antics could be interpreted as just extreme otaku level idol admiration at first... though I kinda doubt they are trying to hide how she really feels, considering a lot of this anime revolves around fans secretly being in love with their favorite idol and the "professional fan" thing just being a facade. And then there were the train scene and some others where Eri was losing her mind, because she was frazzled about the fact that she wants to get closer to Maina outside the idol stuff.
Maina on the other hand didn't reveal much about herself in the early episodes, but in the last 3 or so she's been pretty openly gay in her head and actions. Ya know, this is actually the second time we saw she wants to tell Eri her feelings, because in the reply card that she wrote (but never gave Eri) she also mentioned "I love you".
The only hurdle here is their communication disorder, made worse by their position as idol and fan.