One option could be to check out dedicated manga websites such as MangaFox or MangaReader. Sometimes they have the complete series of Nisekoi. Just make sure the sites are legal and safe to use.
The Nisekoi anime covers a significant portion of the manga, but not the entire story. Some key plot points and character developments are included, but there are still parts left untouched.
Well, in the Nisekoi light novel, it's a story full of love triangles and comical misunderstandings. Raku is at the center of it all. He has a locket which is supposed to match with the key that his true love has. Chitoge is a tough - girl - on - the - outside type, while Onodera is more of the shy and sweet girl. The light novel explores how Raku deals with his feelings for both girls while being forced to be with Chitoge due to the yakuza pact. There are also other characters like Seishiro Tsugumi who add more depth and complexity to the story.
In 'nisekoi ending story', it probably concludes the complex love triangle and other sub - plots. Maybe it shows how the main characters finally make their relationship choices and how their friends and family react to those choices. It could also deal with any unfinished business in the story, like resolving conflicts between different groups or dealing with secrets that were still hanging in the air.