Hi people, I'm back again and this time I'm looking for a manga with one of the lead characters who went to so much that he/she has completely given up trust/love but only to find it again when they least expecting it.
I read all genres so I'll take any recommendation.

Hm.

Skip Beat! - the most obvious example. The main character gave up on love after getting her heart broken in the very first chapter of the manga.

Ren Tsuruga also has given up on love after a trauma in his past. Given that he is the main character's love interest, so they both have problems in this area, you can imagine that their romantic relationship advances at a very slow pace with a lot of difficulty.

Kaze Hikaru - the least spoilery description I can give is that one of the main characters was traumatised after a girl he rejected due to his principles (100% dedicated to the Shinsengumi) tried to commit suicide in front of him. So he then very seriously resolves not to ever get involved with love, or even sex.

It takes 22 volumes but he finally realises he's in love. However for the time being he's still determined to stay away from love, to the point of encouraging a rival to try to marry the person he's in love with. I'm pretty sure his attitude does change eventually, but I've only read the 22 official English volumes, so I can't say for sure. There are scanlations that go further ahead, but last time I checked there was a big gap of unscanlated chapters inbetween.

You might also check out the Anti-love protagonist tag. I guess the Unexpected feelings tag could have some appropriate examples too.

世界のどこかに必ず
キミの居場所がある筈

Poor Poor Lips

~4400 manga completed
~1700 ongoing...

i guess mars counts; it's pretty heavy though

This one kinda dramatic but it's the only one I could think of, hope it helps Deep Love - Ayu no Monogatari and its franchise

DONDAKEE!!

Honey Bitter

Kimi wa Pet

Ane no kekkon