Genuinely, I don’t think we needed that second couple to be a thing or to ever learn about them if this was what we’d get. I would’ve preferred keeping the entire volume dedicated to actually fleshing out the main story instead.

The main couple has a pretty standard BL plot line, a little drama but overall they fall in love normally and are cute together. The secondary couple, however, is where most of those category warnings are coming from. It's definitely a rape turned relationship sort of plot, mixed with blackmail and drugging. It somehow turns out romantic once they sort out their feelings, but it's still such a major 180 from the assault that it doesn't seem reasonable.

Most everyone in the entire manga has some form of trauma, from heartbreak to loss of a lover to phobia responses, so be prepared for drama (some of which is not handled in a way that i would consider to be realistic). At least it ended on a happy note, with everything sorted out.