Alright, let's sort out what actually happened. The only thing you really helped Nauxus with was finding the spy.
As for the rest, from his perspective:
The first time, you promised to help them take over the camp, but it ended in failure. The others with you claimed they never saw you show up—only the phantom of a wolf. You only appeared after they'd already returned and reported back.
The second time, he has no way of knowing you stopped the bomb. All he knows is that he brought you along to persuade the rogue lizards. When he drank poison to prove his resolve to them—after specifically telling you which color flower was the antidote—you still brought back the wrong one. The persuasion failed, and if he hadn't prepared an antidote in advance, he would have died because of your mistake.
The third time, he asked you to retrieve the stolen fruit, and you never showed up again—not even by the end of the festival.
Unlike Thane and Axel, who care more about outcomes, Nauxus is the type who focuses on how you do things. Given everything he's been through, he absolutely despises betrayal—and all of this has left him deeply insecure. If anything, it's a miracle he tolerated you as long as he did. The only reason is that he likes you and kept trying to believe in you.
Sure, you may have eventually helped both sides find their missing children, but by now, he's completely disillusioned with your past behavior. He won't see it as you helping him—he'll feel more like you only helped him as an afterthought while helping the bulls.
The key to building a romantic relationship with him is making him feel like he truly matters to you—like he's more important than others. He won't respond well to feeling like an afterthought, like someone you only helped because you were already helping someone else. He doesn't want that kind of charity.