【TLD】 Information with spoiler (Ep. 46):
Why was Leyr so angry with Thorn threwing him off the cliff?

Leyr was angry at Thorn, not because she threw HIM off the cliff, but because she threw herself off for Victor. Thorn had never done anything that would so obviously lead to death. Every time she risked her life for Leyr, it was in situations that, from Leyr's perspective, were controllable. But jumping off a cliff would clearly have led to death if Leyr hadn't protected Thorn with his sturdier body.

In other words, Leyr was angry at the fact that Thorn threw her own life away for Victor. So much so that he snapped. 😅
It was probably a combination of anger and jealousy.