I think these two sentences are the same. I looked up "go back" and "come back" in the dictionary, and both mean "back to". So is there a difference between them? I don't understand why the writer would choose to express the sentence one way, rather than the other. Is there a reason I am not aware of?
He wants to go back to his wife and children, but he doesn't dare.
He wants to come back to his wife and children, but he doesn't dare.
Both are grammatical and idiomatic, but have slightly different meaning. In the second one, the speaker is in some way identifying with the wife and children, or where they are: probably implying that they and the speaker are in the same community which "he" is currently outside.
This is a systematic difference betwen "go" and "come" in English: "come" almost always means to somewhere associated with the speaker. Canonically it means to where the speaker is now, but it might be to where the speaker is going to be when the subject arrives, or it might be to the speaker's home, or the speaker's town, even if the speaker is not there or not going to be there.
English is so wishy-washy about directions, at least, compared with other languages. In general consider the perspective from the person speaking, or the person being spoken about. For example, if I say:
"He wants to come back to Miami"
implies that I'm in Miami, or I'm talking from the perspective of someone in Miami.
"'I'll come back to you someday, John!' she cried, waving from the window of the departing train."
The woman is thinking of this from John's perspective, some future time when he sees her coming.
In your example, the first sentence seems pretty straightforward. In the second sentence, the person talking is thinking from the perspective of the wife and children, and so it implies some degree of familiarity with the family.
But as I said, this is general use. Sometimes people will use one or the other interchangeably, whichever feels more comfortable.
He wants to go back to his wife and children, but he doesn't dare.
He wants to come back to his wife and children, but he doesn't dare.
In these sentences, neither he nor his mother is the speaker or the listener. So to choose between the first and second sentences you have to decide from whose viewpoint you are looking at the situation:
If you are looking at it from his point of view, it will be
He wants to go back to his wife and children, but he doesn't dare.
If you take his wife's viewpoint, it will be
He wants to come back to his wife and children, but he doesn't dare.
Anyway, both the sentences mean the same thing and I fully agree with @Andrew that it's utterly up to the one who's expressing the idea to make the choice.
