Given the magazine where this publishes and the general tone of the series, this is as far as the author would go to show they had sex. There is not much to overthink here, a college student and his girlfriend (in the last year of high school ) where both are pretty well adjusted and in a healthy relationship spent a week alone together under the same roof, having sex wouldn't be weird or out of line. The series will not dwell or make a big deal out of that, in part to avoid those subjects in a shonen magazine and to keep the focus on them growing as individuals and as a couple.