In volume 13 of Akane Tamura's A Side Character's Love Story, Hiroki and Nobuko finally go on their graduation trip! That's the bulk of the volume, and it's a delight: they spend their usual amount of effort on clear communication and sharing their feelings, and they also follow up on the previous volume's dilemma by finally deciding that they feel comfortable enough to do more than kissing. 

(It's not explicit, by the way -- we see them holding hands and kissing, and we're told that Hiroki was very gentle, but that's as much as we know.)

Hiroki does also tell Nobuko that he wants to marry her, and that feels surprisingly-for-them undercommunicated: he kind of springs the idea on her, and later affirms he will propose to her properly when he graduates. I guess they do swing back to it, and it's clear it makes Nobuko happy, but she was so surprised... I don't think they talk about it again, either.

Strange to think they're at least two years into their relationship -- the volumes have flown by!