I believe that enough character tension needs to happen to be a plot thread that's worthwhile. That only happens through their individual character development. But even then sometimes it works, and some times it doesn't.
If anyone here who is a Marvel fan who has seen Avengers: Age of Ultron, you might recall that there was a plot to introduce The Hulk and Black Widow as a couple. In my opinion it could have worked. However I can see why lots of people didn't buy into it. For one, the two have never really had history in the comics. Two, people thought it was a rushed plot that didn't add any substance to their individual roles in the film. The point I'm making is that sometimes it works, but it has to be convincing and generally accepted by those who are consuming what's going on.
I like to watch the madness unfold of will they/won't they couples. It's a cliché trope, but it's so good when it's convincing. Typically I'm more in favor of two parties eventually hooking up rather than them seeing different people, and yet they still think about each other. That's another muddled mess.
