What you are doing is, you are accepting split response in two different variables, and strings.Split() is returning only one response and that is an array of string. you need to store it to single variable and then you can extract the part of string by fetching the index value of an array.
example :
var hostAndPort string
hostAndPort = "127.0.0.1:8080"
sArray := strings.Split(hostAndPort, ":")
fmt.Println("host : " + sArray[0])
fmt.Println("port : " + sArray[1])