This wiki says that Marimite is all about close female friendships, but the overwhelming amount of subtext has some people unconvinced. Sure, sure, there's only two girl kisses on camera, but with all the admiring from afar, all the demands for some 'service' from Sachiko, the fact the entire campus wanted to score a date with the popular girls (and we're talking a real dinner-and-a-movie date), Sei flirting with Yumi almost to the point of being Once an Episode, the comparison of Rei and Yoshino's split to a divorce, and to top it all off, they made Sachiko's fiance gay in an almost Cleaning Up Romantic Loose Ends sort of way. It's even impossible to watch the ending animation without being just a little suspicious.
The maker of Marimite realizes very well that it's considered yuri and the hints are not coincidental. It would significantly alter the mood of the show though if all the girls would freely hop into bed with each other, although it can get a bit unrealistic that they would show so much self-restraint, considering how much they have been leading each other on already.
Both the novels and the anime make it blatantly clear that whilst Sachiko did love Suguru (her aforementioned gay fiance) when they were younger, he has never reciprocated her feelings and has always accepted his sexuality so there was never any romance between them to clean up so to speak. Their relationship was an Arranged Marriage that certainly in Suguru's case he never really wanted deep down but agreed to go through with for the sake of their families coming together.