Often, there's the theme of a hidden or slowly emerging attraction. They could have been friends for a long time, thinking they were just pals, but then little things start to make them see each other in a new light. And of course, the theme of courage is also there. It takes a lot of courage for them to admit their feelings to each other and to the world.
A common theme is the transformation of the relationship. It goes from a platonic friendship to a romantic one. Also, there's the theme of finding love in an unexpected place, which is right beside them in the form of their best friend. And sometimes, there's the struggle with society's norms and how they break free from those constraints to be together.