One similar light novel could be 'Fullmetal Alchemist'. It has themes of brotherhood and loyalty which can be related to the idea of always being by someone's side. 'Fruits Basket' is also a good choice. It focuses on the relationships between the characters, with a lot of heart - warming and sometimes heart - breaking moments. Additionally, 'Clannad' is known for its emotional depth and strong character relationships.
Well, 'The Melancholy of Haruhi Suzumiya' can be considered. It has a very distinct story - telling style and the characters' interactions are quite engaging. Then there's 'KonoSuba: God's Blessing on This Wonderful World!'. It's a comical light novel with some great character development and relationships that might be similar in the sense of character bonds. And 'Re:Zero − Starting Life in Another World' also has elements of deep relationships and a unique plot.