Haou Airen
This one is just mistake after mistake after mistake and in the end when the guy decides to live better, he's confronted with all his mistakes. The girl didn't deserve this kind of shit to be honest. She would've been better off not meeting the guy.
Visukiisu No Akai Ningyou
Please Save My Earth
It was very good. I really recommend it to people that like more mature and thought provoking manga such as Basara, 7 Seeds, and Tsubasa Reservoir Chronicles
Sheryl - Kiss In The Galaxy
Although this is another version for Macross Frontier, you can fully enjoy this story without needing to have watched the Macross Frontier anime or movie (all of which have different endings and pairings). I read Sheryl years before watching Macross Frontier and even now when I have read and watched all their media, I still think Sheryl was a great read and I prefer the Sheryl story with all the Sheryl X Alto moments over the MF anime and movie that aren't as romance oriented as Sheryl and that had Alto being indecisive in choosing between Ranka and Sheryl.
Koizora
I don't recommend this one to anyone. I only read it cause I kept thinking "How sad can it be?" after hearing people talk about it. It truly was heart-breaking and it makes it even worse to know it's based on a true story. Honestly, if you can help it, go look for something that you'll actually enjoy.
Love in the Mask