I just wanna say two things:
1. Give Mai-chan a gf, she needs one now—or it's gonna be sad—and it's not Nanoha and the author shouldn't have structured the manga like this, instead:
2. The author should've made Mai-chan tell Naa-chan that she has seen Chidori and Nanoha kissing. Then one chapter semi-focusing on Mai-chan so that we get her point of view even more and clearer, but with something added: Mai-chan is crushing on a girl from her basketball club or something, and so that's why she tell Naa-chan that she saw them kissing and that she likes a girl too and that she wants some advice from her. If Mai-chan were bolder, she could actually also tell Naa-chan that she loves/loved her. (If the author were even bolder, she could even work on a polyamory relationship between these three, but understandably that's not the direction the author wants to take). Anyways, this would get us three things: a happy resolution to Mai-chan as a character and hopefully to her new relationship; a good resolution towards the 'I have a chance' bullshit, although I guess Mai-chan doesn't really harbours any bad feelings... yet it's still kind of nonsensical to think like that when it's your friend that is in a happy relationship at the moment and you wouldn't really think of doing that; and a possible way for Nanoha and Chidori to understand that their love may be more common that they think and for them to realise that maybe their friends would actually be okay with their relationship, and so a gradual opening-up of them towards their friends (who, oh surprise!, probably actually know they're dating! haha). Anyways, I think the author could've definitely handled this better and even more differently than 'old Chidori almost-gf' was handled.