I don't know what the author has in mind, but I don't think Maya will do wrong, but rather Ruka will cause it, Maya promised to be honest and tell the truth; truth can hurt too, I think it will make Nemu feel worse and inferior than he is now.
I think Ruka will just try to trigger things but no intentions to break them up or take Maya for himself. Maya will try to pledge innocence to Nemu panicking, which I don't think Maya is. Sorry but Maya will be an ass, I can already imagine. He won't cheat but will also not help appease Nemu's troubled heart. Then the cycle continues, Nemu gets blamed for everything.
Personally, yes Nemu would have a fault there but Maya is not and never will be innocent.
fuuckk that last line seriously got me thinking maya did something shitty and hurt my bby nemu again ;n; but in keeping to his promise, he probably told nemu about his mistake or something