Heh, called it!
I remember thinking that Levi looked kind of stiff when interacting with Lilli in chapter 3. I think I dismissed it as teenagers being awkward, but now? It's not surprising to learn that she initiated it and Levi kinda went along. With this I get the feeling he's having doubts whether he really loves her, or whether she's just cute and having a girlfriend (like big brother Piet does) is cool.
Judging by his face, I'm guessing Piet feels similarly about Thea. "Do I actually love her as I love(d?) Lukas?" "What if I don't?" etc. I can imagine this is a talk he didn't want to have the same day he ran into Lukas for the first time in ages.
Doubts, doubts everywhere...