Why wouldn't it? From what I understand, neither of them mention the lover as "he" or "she" so it's pretty much speculation at this point.
Went and check the RAW:
The story use 'lover' (koibito) throughout until the last one where she specifically used 'kareshi' (boyfriend)
That said unless the author plan to have some weird twisty development the person should be a guy for easier reveal of teh gay.
Why make your loved one suffer and long for you while making her think you already have an S.O. This premise is a bit fucked up for me to enjoy ngl.
The "I got a boyfriend" was basically gay-testing her friend, because at the time she wasn't sure of the other girl's feelings.
The person sadly chose the 'hide teh gay' option so the girl thought her love was one-sided.
This chapter was basically her using that situation to her advantage to kiss the one she likes while trying to hide how big geh she is.
The last page is both her saying with 'confidence' the other girl's gay AND showing how little confidence she has from the shock of the other girl tried to show support of her having a boyfriend before.
Hence the 'boyfriend's final comment, essentially saying 'these dang useless lesbians'