Is 'faithless' a literary version of 'unfaithful' (in the context of a spouse)?

Solution 1:

• a faithless person is a person without faith. For example, an atheist or nihilist or a person who believes in nothing. I would not say a wife or husband is faithless in terms of cheating on each other.

• a faithful person is a person who has faith towards others, often, a spouse, but not only. They have faith in someone or something. They are faithful to someone or something. A faithful friend is one who does not betray you.

• an unfaithful person is one who betrays the faith others have or had in them. If a wife or husband is unfaithful, they are breaking their marriage vows.

• a person can also be unfaithful to something. Unfaithful to an ideal,for example.

As for neutrality, that does not come into play here.

As for literary, they could all be said to be literary.