Peter may initially be angry. He might feel that Maryjane didn't give him a fair chance or that she misjudged him. However, as time passes, he could come to accept the rejection and try to move on, focusing on his own life and other relationships.
In the fanfiction, Maryjane could be in love with someone else at the time. Even if she has some feelings for Peter, her stronger feelings for another person make her reject Peter. Also, Peter might have done something in the past that Maryjane can't forgive, like lying to her, which results in the rejection.
The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.