There was a rather substansial part of Walt that wanted to hustle Brigitte directly off to Pomfrey, or dump her into McGonagall's lap or even write to Clifford right there in front of her, even if he wasn't sure Brigitte's brother had ever heard the phrase "don't kill the messenger."  What he was quite sure about, was that he'd been trying to be nice.  He wasn't in here practicing summoning charms because of some weird course work fetish.  They were friends.  He was worried about her, and she was in here jeering at him as if he was the one who had done something wrong!

“Merlin! You’re not going to let this go. Because it…felt good, okay? Because it…was better than nothing, better than offing myself, wouldn’t you say?”

"But there's nothing wrong!" Walt protested, raising his voice to match hers even as his better sense said yelling at her was probably not the way to go.  "Well? Is there?"  He suspected Eph was being rather less affectionate than previous, mostly because his best friend had been present and accounted for each night by the time Walt got off patrols.  Still, this was hardly reason for her to hurt herself, at least in Walt's mind.  He was more than a little suspicious that Brigitte just liked to make people worry, and he didn't appreciate being a target of her schemes.  "Bloody hell, Brigitte. You need help."

“It’s not doing any harm so just let it go, Walt. Let. It. Go.”

"That's not going to happen." He informed her. He didn't bother asking if Eph knew.  If Eph knew, Brigitte would probably be booked on a port key to Saint Mungos already.  Which wasn't a bad idea, actually.