(adsbygoogle = window.adsbygoogle || []).push({}); Is it because my last follower is dead or because I haven't completed a quest?
im playing on ps3, but i dont find any good answer

It is probably because they died, you probably went far ahead of them and they died without you really knowing. You can go to the Inns and brawl someone in there to get them to be a follower, or simply do quests and I am sure you will find a follower the Companions have a lot of people that you can ask to follow you and they can also train you, just ask around and you will find another follower.

It could also be that you told your companion to wait in a specific spot, and you forgot to go back and tell them to follow you again. They probably became "tired of waiting" and returned to where you initially found them. For example: If you own the home in Solitude and you use the companion that comes along with the house. If you tell her to wait somewhere and forget to pick her up, she returns to your home in Solitude.