I didn't unlock the h scenes with Ayase so I'm not 100% about her stance but I'm pretty sure there is no real attraction there, Miharu gets jealous and upset when she sees you with other girls so there's that. Either way, why complain about it one way but not the other? Double standards. It's not even soft ntr. Nor is it cuckold in any way. It's just a character in a main friend role doing what she literally said that she does and gooners wanting exclusivity.
MC doesn't see her sexually nor romantically. The only time he does is if you choose to fuck her. Which is after she tells you her situation. And even then it is only in that situation. I don't believe the story really shows her in a way that you would want exclusivity at this point in the story. Later on however, MC might develop feelings. But that's obviously going to be WAY after you help her get out of that situation. So again, no ntr. No cucking.