What do you mean by forced relationship? We've got two people who are still in love with each other, one keeping his distance "for the greater good," and the other full of hurt feelings. (Cliché setup, I'll admit.)
Anyway, what she overheard wasn't a misunderstanding. Just him being noble and trying to put distance between them in the rudest way possible, because he was a teenage tsundere. He regrets it immediately, but, you know. "Greater good."
There should be an explanation for his actions in like a chapter or two. I remember that he got a POV scene that explains everything fairly early on in the novel, I think when they spend the night in the church they're currently in. (Literally their first night. It comes up quick.)
Is this going to be one of those forced relationships? Even if it has to do with some type of misunderstanding (which I hope is not going to be the case)