It's because okino says something about "raper/rapist" basically okino is somewhat telling them what happened to him, then Maya got insecure because he had done that to nemu too... So yeah, Maya got guilty about it.
i was just looking at that scene and wanted to write this :D
http://www.77mh.com/201607/336458.html?page=17
Huh well..he does deserve to feel bad about it. I can't say I feel bad about him feeling bad. ╮( ̄▽ ̄)╭ He also never got any punishment for the way he acted in the beginning and Nemu never got any revenge. So if the least he suffers is guilt I'd say it's well deserved.
http://www.77mh.com/201607/336458.html?page=1