What I meant to say * NOT TRYING TO BE MEAN, AND I CAN NOT STRESS THIS ENOUGH BUT NOT TRYING TO BE MEAN
The author might make that happen (since there are already boyish gfs, Iku and Uto) but Rentarou seems to just be straight and I dont think he knows he concept of homosexuality (He still thinks Hakari and Karane are "Very good friends") anyway
The "love" this manga tell isn't that kind of love hence why the title is kanojo=girlfriend not koibito=lover, Rentarou can't break gender boundaries even if he want to.
I know this is crazy for me to say this, but what if the possibility that Rentarou ends up getting a boyfriend or someone who is transgender. I know that's crazy, but considering the many different types of girlfriends, you would think that one of them would possibly be a guy, and I'm trying to be mean, I'm just saying it being a possibility