Despite Marianne's longstanding desire to bring their kingdoms together, when she and Bog were in private, barriers were still very important to both of them.
It took weeks for them to kiss again after their confession-song. Months after that for the kisses to become more intimate than a light contact between lips. Even a year later, despite rampant speculation from their subjects, their physical intimacy was still technically innocent.
They would hold hands, and they would put their arms around each other, and they would kiss, and they were both happy with that.
There was no need for more.