I'm playing The Walking Dead and I'm trying to figure out if there are different endings and who will stay with me until the end of the game. Does gaining reputation help you in the game?
The Walking Dead really only has a single ending, though there is one final decision that can be made near the end that changes what happens to one major character.
The decisions you make during the game do influence a lot small things within the game, however the main plot is the same for everyone. Reputation with characters works the same way - if a character dislikes you, it may change the way they react in certain conversations, but it does not change the plot. You are encouraged to role play Lee as you see fit, without worrying about whether what you are doing will adversely affect the game or not.
As far as which characters will stay with you until the end of the game, I can guarantee that Clementine will be there, but for everyone else, I encourage you to play through the game and find out for yourself.