First guy who ever spoke to me in Skyrim, he was there with me from the beginning, he saved my life, I joined the Stormcloaks, he helped me in the Battle for Whiterun and Fort Neugrad, killed many Imperials together.

I wish he was a follower, he is a good man and warrior.

I thought the same about Hadvar, he would be a pretty awesome companion, I kind of wish he came with you throughout the Main quest.

agreed. i really cared about Ralof. he's a good man.

He's probably too important to be the player-character's lackey.

Babette not a companion? Whyyyyyyyyyyyyyyyyyyyy? Sorry, I had to vent over Babette.

They are soldiers and already committed to their jobs and orders.

After the war is over, Ralof can be found living in Riverwood.

True, but he is still a soldier and has to be on standby in case his superiors call on him (even though it doesn't actually happen in the game).

No doubt someone will make a mod allowing you to travel with him in the future.