I heard chapter 5 changes things so I'm gonna patiently hope it does because right now Eri is one of the most annoying characters I've seen in a yuri manga. Her selfishness and a lack of consideration for others is grating on my nerves. I honestly felt bad for the dude. Why would you accept a confession if you don't feel the same way as the other party does? It's more harmful to pretend than to just flat out reject them, and the guy is ultimately going to end up in the worst position as a third wheel when his two best friends get together after Eri never really gave him a chance and just strung him along.
Senpai is a superior option. Too bad she's gonna lose badly.