Why Nat and Travis _____ __

Ultimately, I think the reason they break up is because Travis sees the girls as directly bringing more trauma to him. Sadly, Nat is part of that.

The night he lost his virginity with Jackie (when he didn’t want to), Javi went missing. He then consumed her body with the rest of the group.

He eventually thinks his brother died, and Nat is the reason he stops looking for Javi. Later, Nat pulls the queen of hearts and is supposed to die. Javi actually dies this time instead. He then consumed his body with the rest of the group.

In the pilot, Coach Martinez is putting Shauna's mask on her while the plane is going down. I think in s1e2 Travis says something like, "My dad fell out the airplane door because he was trying to help one of you idiots put on an oxygen mask."

He blames them for the loss of Javi, his dad, and probably as part of the reason he's even stuck out there in the first place. He saw Nat as a lifeline, but maybe now everyone, including her, is a liability. Now that she’s the leader of the group, he fears what else would happen to him.