I want England hopelessly in love with (for the first time oblivious)France. Of course Arthur being the tsundere we all know and adore prefers to suffer alone and doesn't give away any glimpse of his feelings, except for rare occasional slips. Will France return his feelings is completely up to potential author.

Bonus 1: N.Italy (or Spain) is the one who open France's eyes (having the enormous experience dealing with Romano on a daily basis)