Looks it will be up to our imagination to see how Sagawa managed to confide MC. From the looks of it, it didn't take much convincing or effort on her part. (I mean...who would say no with that body? lol).
Hopefully, MC finds a way to clear his mental state and escape from this situation to make it to the event in time. His friendship with Tomoki and the tennis club is one of the few things that snaps him out of his slave state of masochistic lust. With any luck, Sagawa becomes sane enough to let MC go with a warning after thinking she successfully reprogrammed him to her liking.
As an obedient thrall that she can abuse, then yes. It's hard to tell since Sagawa usually has a cold fish expression whenever she interacts with the MC sexually.
Even with all that treatment it’s good to see he at least wants to get free. A person without his trauma would also call the cops once free, but he’s not strong enough for that. The stuff that’s on their phones alone is probably enough for them to be locked up for a decade.