different between faithlessness vs infidelity

English

faithless +? -ness

faithlessness (countable and uncountable, plural faithlessnesses)

From Middle French infidélité, from Latin infidelitas

infidelity (countable and uncountable, plural infidelities)

Unfaithfulness in a marriage or an intimate relationship: practice or instance of having a sexual or romantic affair with someone other than one's spouse, without the consent of the spouse.
Unfaithfulness in some other moral obligation.
Lack of religious belief.
- 1674', Seth Ward, Seven Sermons
  The means used to this purpose are partly didactical, and partly protreptical; demonstrating the truth of the gospel, and then urging the professors of those truths to be stedfast^[sic] in the faith, and to beware of infidelity.

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