[Rei blushes more and hides his face in the crook of Rin's neck. He knows Rin isn't making fun of him or anything, he just feels a little silly now. That's not even a literal promise (his parents like Rin, but wouldn't be in favor of him moving in permanently), just another instance of his words getting away from his sense.]

You're welcome.

[He takes a slow breath, brings his face away again.]

Maybe you should talk for awhile. Before I say something really sappy.

[He's still not thinking marriage like Rin is, but he's sure he can come up with something else embarrassing.]

Not that I don't mean it, I mean. Of course I mean it. I'm just not used to this yet, this is the first time I've... been in love.

[At least he hasn't said anything about theories yet.]