It's the jealousy, and in ch. 5 Damien found the bruise on Kayden's hip that looked like a hickey. And when he asked Kayden about it, he could tell Kayden was lying when he said he fell from his horse. So, that along with his jealousy have fueled Damien's demons.
Being caught by the hunters most definitely terrifies him. It's his worse nightmare coming true, which is why he's so panicked and terrified right now.