Bokura ga Ita, Sunadokei Recommendations
I think these two mangas are really similar because of two reasons: first of all, in both of them, one of the main characters faces the death of a dear person - but later falls in love with someone who helps him/her to get over it.
Secondly, in the later parts, these mangas deal with long distance relationship.
I highly recommend both of them.
It's about things that can actually happen in real life.
Both follow the couples from a younger middle-school age until they have graduated and beyond, showing both the drama that happens in your highschool years and also the tough reality of living in the real world.
A tale of separation, first loves, bittersweet memories, loneliness, moving on, and facing the future. Both series feature a boy and a girl who love each other but many obstacles hit them along the way. Both series have a "dead" character that goes in between the main couple even if they're not alive. There's also the love rival who deeply loves one of our protagonists.
Both manga are about love that starts at a young and innocent age and blossoms throughout the years they are together. Suddenly, the couple has to part, which begins to cause problems for their relationship. There are betrayals, whether they are from friends or their partner, and there are times where secrets are revealed, and there are characters who don't get to live throughout the story...