[He continues running his thumb over hers at the same steady rhythm. It's entirely possible that the gesture isn't meant only for her, but also for himself. Because it doesn't seem like he has any intention of stopping any time soon.]

And if you really meant to do it...you would have tried to hide it from me. You wouldn't be here telling me what happened, you'd be with...with him, [Whoever this mystery man is.] trying to figure out a way to cover it up.

[He used to do infidelity cases for his uncle's detective agency, remember? He knows how these things typically go.]

I still like you, and I care about you a lot so...even if you accidentally completed a square with someone else, I want to be with you.

["Accidentally" being the keyword there. This would be a very different conversation if she'd done it on purpose. But he knows that she didn't, that she wouldn't...]