You can use three or four nicknames for your boyfriend, one for every mood of his.
I also call him agapi-mou, which is Greek for my love, but also Handsome, geek, my beautiful nerd (haha), and Knight, Rocky-baby (his name with baby on the end 😉 and Romeo sometimes too.
For instance, if your boyfriend calls you ‘kitten’ call him ‘tiger’. You can also use names of popular comic/movie/Television characters, like for instance: Tip# 5: If your boyfriend knows any other language like Spanish or Japanese for that matter, find out a romantic equivalent in that language and use it as a nickname. He knows exactly what to say to make me the most happiest girl in the whole wide world 🙂 He calls me Mrs.