Complex sentence: At first, Tasuku was only going out with her because of her appearance, but after learning that Aguri has always been in love with him before Tasuku even changed his appearance, Tasuku genuinely falls in love with her.
Split into simpler sentences: At first, Tasuku was only going out with her because of her appearance. After learning that Aguri has always been in love with him before Tasuku even changed his appearance, Tasuku falls genuinely in love with her.