That has to be the worst citation in support of an argument I've ever seen. "Standard usage"...is number 6 on a list of different models of faith in philosophical terms? Right. That's clearly what most people mean when they talk about faith.

Also, trusting someone else is the opposite of fidelity to that person, not the same thing.

Regardless, the definition Nietzsche is using is obviously not referring to a trust-based model.

You seem to be missing the point. "Faith" in terms of religious belief is not the same thing as being "faithful" to your spouse.

You're equivocating. Also, that's not a Prisoner's Dilemma. A Prisoner's Dilemma allows no precommittments(you don't expect to get arrested; neither does your partner), and no communication with your partner once the game starts. It's clear that neither of those requirements is true when considering fidelity to one's partner. Relationships are not Prisoner's Dilemma situations. It takes an extreme stretch of the situation, and a skewed placement of values for BOTH players for it to resemble one. If both players can gain more utility from being unfaithful, why not implement an open relationship? If the utility from being unfaithful is high enough(higher than the utility of the relationship itself), why continue the relationship?

Loyalty to one's partner differs in many many many ways from religious faith.

Let me restate: social obligations are not at the core of what faith is. One could believe something without proof if she were alone in the universe. Faith certainly can be a social obligation, and depending upon what it is faith in, could easily necessitate social obligations, but the general idea of "believing in something without evidence" can be done by one person alone, and social obligations are by no means part of that definition.

What religious people mean by "faith" and what faith actually is do not have to be the same thing.

Also, Nietzsche was definitely not confused about what religious people mean by faith. You're just confused because that quote isn't a statement about what faith is, but rather, a statement about the psychology of the faithful.

Except that faith has little to nothing to do with social obligations. Faith is believing something without proof or even reason to believe it.

Unless you mean "faith" as in being "faithful" to your spouse, in which case, that's not even the same thing as what Nietzsche is talking about.