Eien no Labyrinth

The main story in this tankoubon takes up half of the book. The first time Misaki met Eiji NIRESAKI, she was 17 years old, and he was visiting her father as part of some sort of study group. I believe Misaki's father is a university professor or a scientist. There is some chemistry between Eiji and Misaki right away, and before you know it, Eiji announces his intention to marry her. They get married after she graduates from high school, but their romance does not last for long. Eiji begins acting strange, and after only a few months, he leaves Misaki. What is going on with Eiji? It looks like he is involved with some serious things that Misaki has no idea about, things that are keeping him away from her. Meanwhile, Misaki is alone and pregnant... The other two stories in this are about a married couple with a child, and a stylish office lady who has a relationship with a coworker.
(from http://www.piffleprincess.com/sakai)