Michael doesn't want to tell Lee what his plans for the evening are, or ask to go to her art thing with her, or try and see if she knows a word for whatever-this-is, although all of those things try their best to escape his brain via his mouth. The only way he can keep them in is by replacing them with something else, and he hates it because he really doesn't want to say anything at all right now. It's not like they have a lot of time, here.
You could come back late, I'd probably still be awake. / I'm trying to imagine what might happen if I didn't see or talk to you for more than 24 hours. / Pop only ever came here to use the photocopier.