It's a shojo, by Mayu Shinjo. It's sold in any book store that has manga. I have up to book 5, just got it. I love how Sakuya loves Aine unconditionally, and she's so not used to someone protecting her. I hate what her schoolmates try to do to her when they find out she's with him. But he ALWAYS saves her in the knick of time. Just like her own personal body guard. And oh, how he guards her body!
They don't have sex until towards the end, maybe the middle, of book 3. It has good romance that leads to great sex. It's cute, funny, hot/steamy, and tearjerking at perfect intervals. I have nothing bad to say about this work of art, but ppl tend to not like how Aine isn't "super-model beautiful", while Sakuya so is.