Meredith couldn't believe that Brayden kept talking to women when he had explicitly told her he wouldn't and to top it off it was in the middle of the night. She had already dealt with Mizuki, which she was actually kind of disappointed about because she had really liked her when they first met.
Most things are too good to be true. Like her marriage or Death Contract that chained her to this man who said she was a reflection of him and he would never let any sort of scandal reflect on her and thus indirectly on him as well.
Meredith had that little nagging voice in the back of her mind that told her to trust Brayden. But she ran for hours on the treadmill so that she didn't have to listen to that voice. She knew what had happened.
There was no denying it. Brayden had received a call around 12:30 a.m. and woken the both of them up. He answered it. Meredith had wondered why he hadn't put his phone on do no disturb mode.