How did we get here?

In one of my parties, there is a player couple(cleric and monk), however their characters are not in a relationship. The party’s bard has gotten the attention of the cleric. At first, it was just two characters getting along well and it made sense considering their backstories and direction the players were taking their characters, that they’d be friends. But then it got flirty. Which, as the dm, I kind of tried avoiding as best I could just to avoid any unnecessary drama, but the other players were all for it and because it made sense they just kept playing into it. I have noticed it makes the monk uncomfortable when these flirty scenes play out so I try to direct them toward something other than just flirting but then I was accused of railroading and so I talked with the three players and wanted to either establish and end to it or if it’s okay then it’s okay. The monk said it’s okay. Most recent session, and a more romantic than just flirty moment happens and the monk is obviously upset but trying to hide it. I made a comment above table saying “let’s consider everyone at the table.” And everyone said they thought it was great and the monk shrugged and said yeah it’s fine. But it’s obviously not. What do I do? Let them play and risk drama or cut it out?