@Lilliwyt I'll somewhat defend Nanoha here. From her perspective, Chidori has been whispering with a mutual female friend, and when Nanoha asked a reasonable question about what they talked about, Chidori responds by blushing and saying "Its a secret." I'm sure Nanoha trusts Chidori, but its still a rather alarming thing to hear from your girlfriend. I think its entirely reasonable for Nanoha to be a bit upset, and want to have lunch away from Chidori to calm down before trying to talk with her.
That said, Nanoha shouldn't have tried to tease Chidori while upset. That's never a good idea, since your actual anger tends to bleed through and it makes the "joke" look mean or petulant, as happened here. And I think Chidori has every right to be pissed about Nanoha doing that, especially in public. I'm not arguing that Nanoha is the victim, rather I'm arguing that the blame here is closer to 50/50 than 80/20. That makes for good drama, in my opinion, and is why I like this arc.