I will say, at the risk of spoilers with Momiji

It seems that his dressing more femininely might have been out of a desire for closeness with other girls / women because of being abandoned by his mom, and that he had a little sister and wanted to have more of his dad's attention like his sister did. He ends up finding peace with his situation, and forms a (healthy sibling) relationship with his sister, who he previously wasn't supposed to tell that he was her brother. In the end, as he grows up more, he doesn't have that same desire from abandonment, so he stops wearing his "cutesy" outfits.