Katsuai no Ouji-sama

Koyuki started dating a super handsome guy named Kanomitsu, who is known as the Prince of Ice because of his cold words and manners. Being touched by his true kindness and straightforward love, they were able to live a peaceful life, until his brother suddenly makes an appearance. That's when she discovers the truth of what had made him lock away his heart…

Also contains two extra oneshots n the volume

Ch 5: Aioki Koi no Hajimari

Ch 6: Yume Miru Koigokoro