[ . . . viola lets her hand rest over byleth's]

When you care for someone, you wish for them to be well. What happened - no matter how he's getting better or healed now, did not treat Dimitri well.

You don't need to say it's fine, or that you feel fine, even knowing he's safe now or that he'll be looked after later.

To feel negatively is simply proof of how much your heart cares.