Let's Talk About the Barn Scene - Again!
Offering an alternative interpretation that may hit the right spot for some of y'all.
In most real cultures - both historic and today - people really don't care about boys and girls spending time together until they're at an age to "get into trouble", at which point parents start to get concerned. In historic cultures (and some cultures today), this is the age when a wall has to go up between girls and boys. At the time of Phoenix Gate, Clive was certainly past that threshold, and Jill was approaching it quickly. It's fairly safe to assume that some combination of Elwin, Rodney, and whatever other instructors Clive had in his life would have taught him that he needed to treat Jill "like a lady", keeping his hands to himself, no funny business. Clive, being the boy scout that he is, would have adhered to the rule like his life depended on it, and would have probably expected to adhere to that rule until/unless they became formally betrothed and married. Based on how Jill treats Joshua and Clive, she probably did not have those talks (though based on her physical maturity level, she would probably have gotten similar talks in a year or so).
When we get to The Barn Scene, it's been thirteen years, but Clive has probably never reconsidered the rules he was given because they've been completely irrelevant for the vast majority of said thirteen years, and during the few days that Jill has been back in his life and conscious, he's had a lot of other things to think about. So when Jill nudges his personal space - something she was never specifically instructed to not do - he defaults back to the rules he had been taught as a teenager: keep your distance, hands to yourself, don't do anything you wouldn't do in front of your parents, etc.
We can tell at the end of the second timeskip that he has realized that these rules don't apply any more, and he's much more tactile with her.