What are the differences between faith and fides? What are the differences between faith/devotion and fides (deities)?
There was a discussion of "faith" in Buddhism in these topics.

My summary of this answer is that "faith" in early Buddhism is similar to the faith you have in a doctor: you take medicine because you believe it will work, because you hear it will work, because the doctor recommends it.

The fides you mention isn't a Buddhist term, is it, nor a translation of the Buddhist term? I think that the Latin word fides implies the kind of faith you find in faithfulness: if you're a "faithful husband" or wife, for example, then I think that means you make yourself reliable, predictable, trustworthy, constant ... keeping promises ... you see that in the English word "fidelity".