Harry could be very polite and respectful. He may bow slightly and say something like 'It was my pleasure, ma'am'. Since he has good manners, this would be a likely reaction.
He might be a bit shy and stutter out a simple 'you're welcome'. Harry is often modest in such situations.
She might be shocked at first. Fleur is used to beauty and perfection, and Harry's scars are a sign of his many battles and hardships. So she could show a moment of wide - eyed surprise.
Harry could be flattered. Fleur is considered very beautiful, and for her to show interest in him would boost his self - esteem. He might stammer out a response, something like 'I - I'm honored, Fleur.' while blushing furiously.
Well, Fleur is a complex character. When she finds out about Harry's abuse, she might initially be in disbelief. But once it sinks in, she would feel a deep sense of sympathy. Fleur might use her own experiences to relate to Harry. For example, she has faced prejudice in the wizarding world due to her Veela heritage. She could draw on that strength and determination to help Harry. She may offer him a place to stay away from his abusers, and use her magic to create a safe and comfortable environment for him. Also, she could start training Harry in some defensive magic so that he can protect himself in the future.
At first, Harry would likely be shocked and angry. He's used to being in dangerous situations, but being kidnapped by Fleur, someone he thought was an ally, would be a big betrayal. He'd probably try to fight back immediately, using his magic if he could.
Harry might be a bit flustered at first. He's not used to the attention from someone like Fleur. He could be shy and a bit unsure of how to handle it.
Sometimes, Harry might use the rejection as motivation. He could focus more on his training or other important tasks at hand, like fighting against the Dark forces. He realizes that he has bigger things to worry about than a failed romantic pursuit, and this rejection could fuel his determination to prove himself.
He might become withdrawn. Harry has been through a lot in his life, and being heartbroken by Fleur could make him retreat into himself. He may avoid his friends and isolate in his dormitory at Hogwarts.
Harry might struggle and try to break free. He is a brave character and doesn't like being restrained, so he would likely use his physical strength and magic skills, if possible, to get out of Snape's hold.
Harry could be heartbroken. He might isolate himself for a while, not wanting to see anyone or do anything. Just staying in his room, crying and reminiscing about the good times with Edward.
In some fanfictions, Harry might become very angry. He might feel that Ginny is being unfair or not understanding his situation. This anger could lead him to say things he doesn't really mean in the heat of the moment. However, deep down, he's really hurt and confused.