They have their first time in the spring after her mom deliberately blue-balls them on a family trip where Maki accompanies them. She's still quite salty about allowing this current sleepover while thinking the two of them have been officially dating since sometime before the accidental sleepover at his place (she referred to him the next morning as "kareshi" and neither of them corrected her), so knowingly delays things for them by a few days -- days where Umi is so desperately horny that she almost makes Maki take her in broad daylight on the side of a mountain. But she follows this up by dropping them off together after the trip at Maki's place and taking his mom out for drinks all night with an implied wink.
Marriage has been discussed (and so have kids, a bit), but that'll come after uni. Maybe it'll be in the WN/LNs, maybe not.
Done told ya we don't play those Heisei/Showa games in these here parts, pilgrim.