Harry may also struggle with his own identity and self - worth in this situation. He might feel like he's losing a part of himself by being forced to please someone else. But at the same time, his love for Sirius and the greater good of the wizarding world (if there are underlying reasons related to that) could make him continue to endure this strange situation. He could go through a range of emotions from frustration to determination as he tries to navigate this new and unwanted role.
As time goes on, Harry could start to explore what it means to 'please' Sirius. He might recall their past relationship, the things Sirius likes and dislikes, and try to use that knowledge to his advantage. He may also feel a sense of loyalty towards Sirius that, despite the odd circumstances, makes him more accepting of the situation. For example, he might remember Sirius' love for adventure and try to engage in some magical adventures with him in a way that 'pleases' him.
He might be extremely hurt and confused. Harry has always seen Sirius as a sort of father figure, so being disowned would be like a huge blow to his emotional stability. He could become withdrawn and start to question his own self - worth.
Well, he might be in shock at first. I mean, Sirius is like a godfather to him, so the idea of marrying him is completely out of the ordinary. He could be filled with disbelief and confusion, not knowing how to even begin to process this strange turn of events.
Sirius would probably be very worried and immediately try to help Harry. He might use some basic healing spells he knows.
Well, their relationship would be in tatters. Harry would probably avoid Sirius like the plague after such an event. Sirius, on the other hand, would be at a loss for how to deal with what has happened. He might feel betrayed, even though he knows Harry was forced. This would create a huge rift between them that would take a lot of time and effort, if ever, to mend. It would also change the way they interact with other characters in the fanfiction, as their relationship was an important part of the overall story dynamic.
Harry might be initially shocked. He could feel a mix of sadness and a sense of responsibility. After all, Sirius was like a father figure to him.
He might be very sad at first. Harry has always valued his friends, so being forgotten by them would be a huge blow.
Harry may also feel a sense of adventure. Despite the situation, he's used to facing strange and dangerous things. He might start to think about how he can use this situation to his advantage, like finding out more about his parents or the secrets of the wizarding world that Sirius might know. He could be a bit excited as well as scared. For example, he might be thinking that this could be a chance to get away from the Dursleys for good.
On the other hand, he could feel ashamed. If he realizes that he has truly made a mistake, seeing his father so angry and disappointed could make him feel bad about himself. He might lower his head and not say anything, with a look of guilt on his face.
Harry would probably be quite resentful at first. He might think Snape is just being his usual unfair self. So, he would be sulky and do the tasks reluctantly.
He could be shocked. Maybe there are some fanfictions that take a very dark turn or have unexpected pairings that he never thought of. He'd probably need some time to process such strange ideas. And he might also be curious to see how far the creativity of the fans can go. He might even get some new ideas about his own life from reading some of the more imaginative fanfictions.