original meaning : walk with you side by side derived meaning: go through thick and thin together

The phrase means "be together from the beginning till the end of a journey". Literally, we also use this to say the facts that someone stands beside you all the time through all the ups and downs no matter what happens .

go along with you all the way

Walking together on the way. Nowadays,we use the phrase to describe some people do something together from the beginning to the end.