It's this one word that tips Maxwell off to learning that something isn't right with Anna. When he expresses his confusion at her calling him "husband" - because last he checked, they weren't married, and they had only just gotten to saying they loved each other (or, rather, he had gotten to it anyway). Still, she had said it as if it was the most normal thing in the world to call him that.
That was the first little red flag. The second came when she tried to tell him that she could fly, and that she wasn't sure if she could touch him or not, because she might hurt him. That she'd have to go see a friend, touch him, and then know if she was safe to be around. His confusion grew, because it made no logical sense to him. People can't fly, and people certainly don't harm others just by touching them. He tried to laugh it off, and told her to drop the act. She got offended that he thought she was crazy.
The next red flag came when she asked him to come back over to her house. There, she brought him into the garage, where she lifted a car as if it was the most normal thing to do, and he frantically searched the garage to see how she was pulling that trick off. Because it had to be a trick. The law of Physics just didn't cease to exist because she willed it -- even he didn't have that power (though there were times that he wish he had). He kept telling her to drop the act. To admit this was one big joke, because he refused to trust his eyes. Despite the fact that he was a man of logic, that if you saw it, it usually was true, and you didn't get four Science degrees by not investigating the impossible.
But for some reason, he couldn't deal with it. It nagged at him, because while in some way he was getting what he had wanted, this wasn't how he wanted it. Not when she didn't seem like herself. Not when she was calling herself another name, was talking different, was acting different. Not when he couldn't figure out why things were so off...
...and yet kind of familiar. It was the fact that this felt sort of familiar that it scared him. He had no recollection as to why it seemed familiar, and that was what scared him most of all. The memories that he couldn't remember, the lost weekend in January he could never recover but always wanted to -- and here she was telling him everything like she remembered it clear as day. He had no reason to believe she didn't know what she was talking about, because he knew when she was telling the truth and he knew when she was lying.
Yet, he was still unable to comprehend. He was unable to allow himself the acknowledgement that somewhere he knew what was going on.
He wanted to understand, or so he said, and she wanted them to be normal. A walk in a park with her glove-covered hand holding onto his turned into an attack from men in black and purple hoodies that he didn't recognize. Men that for some reason didn't focus on him as much as they focused on her, and after being punched in the nose and knocked back, Max looked up in horror to see her lift a man by his neck with ease, and somehow drain the life out of him, dropping him like it was nothing.
Science didn't allow that. The laws of the universe didn't allow that. There was no such thing as people with powers, not in this world. Maybe in the fictional ones that she was now claiming they were from, as she frantically tried to get his attention, trying to get him to understand.
A broken nose, a bloody dish towel, and a defeated confession later, he asked her to leave him alone. That he needed to get out of the city. That he couldn't be around her, because she was right - she was different. She wasn't the woman he loved. And yet...
...and yet, he couldn't bring himself to leave Boston. Maybe it was that he felt more alone now than he ever had before, and the realization that she was all he had was one that hit him hard. Maybe it was the nagging feeling he had, that he knew she was telling the truth, that he felt it was true, even though he so badly didn't want to believe what he saw. That she'd be capable of what she did. It was...astonishing, and powerful, and oddly beautiful in a way that commanded attention and scared him.
And it made him want to know more. To understand it. To try to be a part of it. She claimed she was like him, and it made him curious. He knew of her second name, but knew nothing of his. He only knew that he was connected to her with his other persona; perhaps giving reason to 'Husband', giving reason to January, giving reason to the messages he had memorized but long since deleted.
So he knew he couldn't leave. Not when his curiosity was now piqued. Not when he felt he had an obligation, maybe even a scientific one (whether if that was true or not, that remained to be seen) to see this through.
After a day and a half alone with his thoughts, he sent her a text, asking if she was okay. A question he knew the answer to, but it was easier to open the dialog back up.
He had never let the unknown get in his way before, and he refused to let it start now. He just didn't want to lose her over something he didn't understand.