This is a shoujo manga. I think the main character is name Maki, she started to date a guy . His ex-girlfriend get some boys to rape her. The she get pregnant after having sex with he bf, then she looses the baby and then she breaks up with the boy friend because he likes to get high. Also the ex-bf gets a new gf.

If you know it, please tell me and thank you.

Also it is based on a true story, or so i have read

that would be Koizora~~

Thank you thank you thank you x100