I had checked it out previously so I'll copy/paste a comment I made on Dynasty forums about it:
"It's at 6:50 of episode 3 if anyone wants to check. Himari uses the term "koibito", which to my knowledge is gender neutral and often translated as "lover". Miki talking about it also sounds gender neutral...but somebody who actually understands Japanese should verify my amateur understanding."
Nobody Japanese fluent ever responded in that thread to help clear up the confusion.
It's been years since I stopped using Dynasty so I'm unaware of their posts. In the anime she's using "aitsu" (koibito is completely neutral, so the translation is dependent of this term), that term is normally used for male partners, which is the counterpart of "yatsu", that's why it's translated as boyfriend. The thing is, nowadays "aitsu" is not only used to refer men, just someone you know well and in informal situations (or just in a derogatory sense), and nowhere in the manga or the anime that ex-partner is given a name, sex or even referred again. Considering yuri is completely normal in this series, a female partner is completely plausible, both language-wise and story-wise. If it wasn't specified is because this was not deemed important, and considering men are almost non-existent in most yuri series you can assume it was a girl, so unless the author decides to determine who was this ex-partner it should be assumed it was a she.
Now, regarding this moment people seem to be confused, Momoka telling Miki "to hold onto those feelings even if they're never rewarded" means that holding her dear nonetheless is what true love is for her, since she still loves Hajime's sister after all this time (for the last bubble I would have translated it as "is that not an option?"). I don't expect Aki to break up with Shiho or try to date both at all, my guess is that Miki will end up confessing but will resolve to move on, dating Aya or not is up to the author.
