In “Welcome Home Frosch” I think Gray and Juvia were on a date.
In this panel, although the term date is not used, it is implied when Juvia makes it clear they will be alone if he accepts.
He says “mmm”, which shows thought or pause and he says “I feel kinda hungry now”.
He understood her condition and accepted it.
Of course, it has been shown time and again that they work well together and have no issue being around each other.
However, Juvia was clearly asking him out. She was doing nervous twisting and taking pauses in her speech. This shows that this is not normal for her to ask. And even if it is, her implications behind it are not. Juvia was asking for a date. Gray accepted.
I am not sure if he understood that it was a date, but what I am about to post will make that irrelevant.
She boldly suggests a date this time. There is no guesswork to it.
She outright said “Let’s go on a DATE”
Can’t spell it out for him any plainer than that.
He responds with “Now?!”
He asked if she meant right now.
He didn’t tell her no.
He asked if she meant right then.
So, they could definitely have been returning from a date.
Dates don’t have to mean you are boyfriend and girlfriend.
I could imagine Gray swearing it’s not a date.
It’s just a theory, not fact. :)