It's called friendship, and Lucy's a pushover so of course Natsu will react like that. If Lucy was more like Erza, and Natsu still reacted violently, then you may have a point.
And as I said, Lucy doesn't scare him like Erza does, and he's spent enough time with her thanks to quests, so of course he'll hang out with her and feel comfortable sexually assaulting her, especially when she rarely beats him up. She's still quite a pushover unless she's beaten him up more often.
It is deluded because even if he's interested in Lucy, he hasn't said or done anything about it. That's the key, and until then the ship is just headcanon, a fan's delusion. He's shown more romantic feelings towards Lisanna when they were younger than he has to Lucy.
And as I said, Lucy doesn't scare him like Erza does, and he's spent enough time with her thanks to quests, so of course he'll hang out with her and feel comfortable sexually assaulting her, especially when she rarely beats him up. She's still quite a pushover unless she's beaten him up more often.
It is deluded because even if he's interested in Lucy, he hasn't said or done anything about it. That's the key, and until then the ship is just headcanon, a fan's delusion. He's shown more romantic feelings towards Lisanna when they were younger than he has to Lucy.

NaluFTW




