In this fanfiction scenario, Snape might be under the influence of a dark spell or some form of blackmail. He kidnaps Harry as a result. However, Harry, being the resourceful character he is, might start to figure out Snape's true situation and try to help him break free from whatever is controlling him.
Well, it could be that Snape has some false information that makes him think Harry is in immediate danger from the wrong people at Hogwarts. So, he kidnaps Harry to protect him. Maybe he takes Harry to a secret location like an old, abandoned wizarding house in the Forbidden Forest. There, he tries to figure out what to do next while Harry is really confused and angry at being kidnapped.
It could end with Snape realizing he was wrong. He apologizes to Harry and they form an unlikely alliance. They return to Hogwarts together and Snape has to face the consequences of his actions from Dumbledore.
Well, perhaps Snape has some desperate reason. Maybe he's trying to protect Lily from the Dark Lord in his own twisted way. He might think that by taking her away from the wizarding world for a while, he can keep her safe from Voldemort's reach.
It could end with Lily escaping and being forever angry with Snape. She might cut all ties with him and go on to marry James Potter, with Snape left full of regret for his actions.
Another way Snape could comfort Harry is by standing up for him in certain situations. Maybe when other teachers or students are being unfair to Harry, Snape steps in and defends him. This act of protection can be a great source of comfort for Harry, as it shows that someone is on his side even if they have had a rocky relationship in the past.
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.
He might also use his wits and knowledge of the wizarding world. For example, he could use a vanishing cabinet or a secret passageway that Bellatrix doesn't know about. Since he has spent a lot of time at Hogwarts, he may be aware of some hidden routes that could lead him to safety.
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.