I agree with
@CBFlap. I thought so for quite a lot of chapters but their relation is just non-existent. All we now is that Narumi is sometimes at Hirotaka's place when he plays video game but that's it. And that's something any friend could do. I personally just tell myself they actually act somewhat as a couple but it isn't really the focus because the manga is more axed towards the comedy than romance part or something but if it stated at some point that there relationship is nothing more than what we see then I might just drop it because that would be quite ridiculous imo.
And also of course they are supposed to be the main couple, if you have doubts just read the synopsis, but it sure has drifted quite a lot from that. This manga as it is now doesn't have much to do with it or even with his title sadly.