Niewiara - meaning

When using "niewiara" in a non-religious sense, i. e. as "infidelity", does it necessarily mean "sexual unfaithfulness" or can it also mean the breach of some moral obligation in a friendship?

Thank you very much in advance for your answers!

For "sexual unfaithfulness" the word is 'niewierność' od 'zdrada'.

It means neither. This is the meaning of "niewiara":

sjp.pwn.pl/slowniki/niewiara.html

1. not believing in religious dogmas
2. lack of faith in something, lack of trust towards someone, something