They're still counting all on "what Peter did". Remember, after this issue we're supposed to be mad at
Peter, not MJ.
So if he throws a tantrum and acts (even more) out of character in this run, they would count on that aspect to justify MJ "moving on" from him. It's their way of telling us "See? She was right not to wait for him and treat him like garbage afterwards because he deserves it!"
And on the other hand, if MJ lied to him about this and he still reacted the way he did, that means they character assassinated him for no other reason than just to make her hate him.
The funniest thing is regardless of what the full context is, none of this seems to explain her reactions right after she saw him back. She had no reason to be mad at him at that time(unless because "he was gone for a long time") and she still looked like she was ready to strangle him when he asked about who the kids were.