I don't know how someone can love someone so much (HANUMAN)

So I am that kind of person who really doesn't care much about people as much i hate to say it we here might be talking about close ones. But one thing that has always bothered me is why Hanuman ji was such a devotee of Shri Ram. Like why would he go all the way to burn down Lanka for him. Why bring down a whole mountain. Who would bother this much. I really want to know don't tell me he was like God to him or brother or father. What I want to know how can someone have such depth of love for someone. It is as your every breath is for that person. WHY and how .