Miscommunication is already a sign of a gonna-be toxic relationship, dishonesty, lack of trust adds more to that. Hell Nemu already feels worthless comparing himself to Ruka. Maya ain't a mind reader, but he should be aware of how his partner feels. Imagine if you're in a relationship, you show your lover that you're uncomfortable of who that person hangs around with, but that person show's no sign of interest. What if all that person talks about now is someone else? One might think that the other party is a close friend, others may think otherwise. That otherwise will, trust me, drive you to be suspicious, therefore needs clarity. Then that other party comes by and tells you you're not worth it. Does it not drive you mad? You can't just bear with it and say, I'll hang on 'til the end.
Been there, done that. Left crushed and am now living with trust issues...
Sorry for ranting.
People really think their relationship is toxic? OMG! Where? Since when does miscommunication and a bit of insecurities equals toxic relationship? They are healthy. Mya isn't a mind reader folks. Nemu isn't being straight up about how insecure he is. Maya has a lot going on. It's natural that he doesn't completely get it. Besides him not telling Nemu about meeting up with Ruka proves he isn't completely oblivious. Stop being overly dramatic. Their relationship isn't perfect but they are good for each other. They both have grown from their starting point. Maya also feels a bit insecure himself because of his "active" past. He probably feels ashamed of his past behavior and doesn't want Nemu to get disgusted with him.