Student or Learner
I'm looking for a synonym (an adjective / a noun) for "not keep one's promise". For example we say, "James is a good and loyal friend but sometimes he can't keep his promises." I just want to say he is a little ... . A word that is not very strong, something that we can use for minor cases.
Another example: I remember we wanted to go camping and one of my friends promised to bring the tent, but he forgot. I think it's not good to say he broke his promise or couldn't keep his promise.