He could tell her humans have been having sex for centuries without the concept of marriage attached to it to signify the righteousness of it. However, he has some understanding why a person might not think their soul is light.

If she were to grab on to him, the result would probably not be what either of them expect and would be at somewhat passionate on his part. Firstly, food is unappealing only when he is an angel. Second, the quality he's had when he was human pales in comparison to Lucy's love language, even leftovers. He won't feel slighted over whatever she decides. He nods his head as if he understands it a little. "When you put it that way," he starts. His stomach rumbles more calmly the second time, which prompts another nod to her. "I believe that is what my stomach is trying to say, yes." Or his cravings. It's really unclear at the moment.

First she wants him to wait, then she indicates for him to follow; Cas stands on his feet, of course, without thinking too much about the mix message. "It sounds like I should go with you. I was not aware you were hungry too."