It's probably something really dumb, like he stained the edge of a new shirt she bought him, so he carefully hems it/tucks it in/tries to pretend it doesn't exist. More important things he would feel obligated to tell her about.

When it comes to Theresa, he's fairly easily embarrassed. His sense of loyalty is pretty much 100% focused on her, and he wants to be a good Earth boy. Perceived misbehavior flusters him, and although he has cried in front of her before, he doesn't like her to see him unhappy if he can help it.

How would Lindsey feel if Sam expressed interest in adventuring and guilds?