Yi Chen always judged people by their actions, not their hearts. Although the Yin Spirit Empress was a holy maiden of the demon sect, he had never heard of any misdeeds from her, and since she wasn't a demon or ghostly entity, he naturally wouldn't yell 'kill!' upon seeing her.
It was just about some food, after all.
And she really was good-looking, and his perception of malicious intent didn't detect any significant murderous aura...
After several conversations, he began to regard her more like a spoiled young lady with rather unique principles.
She had the looks and the brains—without any real guile, and he easily coaxed a lot of words out of her.
In the cultivation world, the ancient virtues of fidelity were not in style; men having multiple wives and concubines, or women having several suitors wasn't seen as odd. It didn't come to the point where if someone took a look at another, they either had to marry or one of them must die.