Use your imaginations. Maybe it's not showed, but it's obvious that sooner or later, Sable will think of them as a possible partners. He just repeat the things about friendship and such because, in his own opinion, completing the whole "school route" without having to think of another matter such as a "girlfriend" is more important than anything else, just that. It's obvious that he will end up with Lisha in the end, surely after finishing the school; it's obvious that he will end up with Eth at a certain point, or maybe always after finishing the school; it's obvious that he will end up with Drakan at some point, or maybe always after finishing the school; with Jorou the only happy ending that she have, surely at one point they will get more intimate, who knows.
It's not your classic average visual novel character who after a while doesn't think about anything, besides getting that girlfriend and such, leaving outside the school, study and everything else. I mean, again, he will be busy with that, with The Hunt and such so it's not really a plausible thing giving him a girlfriend if he doesn't complete, before, what he needs to do. Especially because of The Hunt itself, since it's so dangerous like it was explained from the third year and forward, so again having a girlfriend to deal with in the meantime, can only be a pain in the ass for him. With this, I don't say that he doesn't feel anything for the girls, being friendship and/or even love for them, but simply that he doesn't.. consider the "love aspect" a necessary thing for now. At least this is my interpretation of this char.