Theres this boy i like and he has no idea, hes super nice to me.. but he has a girl which he hella likes..?

and im kinda jealous and i find myself startin to act hella mean like kinda ignorin him just cuz i can't have him? is that bein hella immature? should i stop and just continue to be a good friend to him? i cant help it tho im so jealous...