HAHA
well like I said in my one-word response, he thinks he has a duty to protect Lady Liadrin because she IS of his people and she IS so highly respected. He's aggrieved by her proselytizing, but part of that is because he might be an eensy teensy bit jealous that Liadrin has such a good, solid relationship with the Light and he doesn't. I think this stems from the fact that they both felt the Light's grace and were offered redemption, but Koltira feels that even though he was given a second chance, it came too late. As he said in the manga, a snake shed of its skin is still a snake, and that's how he thinks of himself presently.

But even though their interactions are contentious, he is fiercely loyal to her as a sin'dorei and he knows that she means well, and that she is also trying to recover from past sins. I think he's just mad that she's coped so much better than he has XD