I'm looking for a manga which has a break up or divorce but they realize they still love each other and get back together OR it's too late and one of them has found someone else.

Try http://www.mangaupdates.com/categories.html there are about 400 manga's

Live for something otherwise u'll die for nothing

Welcome to MU! There are only three manga that I remember off the top of my head but they should fit your request perfectly.

Boku to Watashi no Henai Jijou by AMANO Shiro
A rising rock star asks his girlfriend, who aims to become a baker, to break up because of his career. Being a very understanding person, she agrees and they part with each other on friendly terms. However, they still have lingering feelings and soon emotional confusion ensues... A light, amusing story of two people who know, yet don't know what they really want.

Broach, the third one-shot from IKUEMI Ryou's Assari Chocolate
A well-told short story with a realistic take on a failing relationship. The acclaimed female mangaka portrays sensitively the characters' feelings of insecurity and wistfulness, so it's easy to relate to both of them.

Egaku nara Happy End by OZAKI Ira
A sweet one-shot about a long term couple who'd rather split-up than keep an unstable long-distance relationship. Before parting with each other, they decide to go on a last trip. A bit generic but enjoyable, nonetheless.

If you haven't done it already, use the Genre Search or take a look at the series tagged with Breakup/s or Divorce.

[color=#8A795D]"Stories are what death thinks he puts an end to.
He can't understand that they end in him, but they don't end with him."

• Ursula K. Le Guin, Gifts[/color]

To be savoured:

• Blood Alone by TAKANO Masayuki
• Otoyomegatari by MORI Kaoru
• Gangsta. by Kohske
• Seishun Kouryakuhon by AKIZUKI Sorata

Ah, I always have a hard time, because the break ups are seldomly done well (in a realistic way) in Mangas or Manhwas, although spontanously, I have to think of...

Strobe Edge.

This Manga includes actually the only "beautiful break scene" IMO, since the characters (the male lead & his first love) come to this conclusion after realizing, that there is no other solution after changing during the process of growing up. One character starts to like someone else, while the other finds out, that the future dreams don't match and there is no way to force feelings. So, in the end they stay friends and go their own paths, but don't stick happily together, since not every feeling is sorted out right away.

"It's like love is a bonus in your life. Even without it, I'm just fine. I don't feel like pointlessly searching for it. You don't have to make yourself unhappy." (Ookami Shoujo to Kuro Ouji)

"Why does it rain?" - "To create drama." (Drops (Andou Yuki))