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".
There are two levels of faith. If by fides, what you meant was ‘good faith’ or ‘trust’, then it is the “unbreakable” faith (saddha) in Buddha, Dhamma, and Sangha, that is the other level of faith. The two types of faith that is described in Buddhist teaching are:
Blind, irrational, baseless or rootless faith – amulika saddha; and
Confidence based on reason and experience – akarawathi saddha.
The Buddha asked his disciples to not blindly follow him or his teachings but encouraged them to question, explore and investigate them in order to develop confidence in the teachings through experiential verification. Faith or devotion associated with strong emotions (amulika saddha) will not last long, and can become an obstacle to the disciple’s spiritual development (such as in the case of the Vakkali Thera, who was enamored by the Buddha's appearance). The Buddha admonished Vakkali, stating that “The sight of my foul body is useless; he who sees Dhamma sees me, yo dhammam passati so mam passati; yo mam passati so dhammam passati.”
Unlike faith-based religions where faith is a significant factor for salvation, in Buddhism devotion alone will not help one to attain Nibbana. In the Vimansaka Sutta of the Majjima Nikaya, the Buddha encouraged monks to critically inquire, investigate and clarify what is said as that would lead to the development of confidence based on investigation and conviction.
A disciple with strong faith but weak wisdom (panna) may remain in blind devotion with poor progress while a disciple with strong wisdom but weak faith may become too rational and cunning which would also hinder spiritual progress. The five spiritual faculties of Confidence (saddha), effort (viriya), mindfulness (sati), concentration (samadhi) and wisdom (panna) become spiritual strengths or powers—bala—when they have become unshakable and strong enough to control any opposing factors.
There exists a Conventional Truth and an Absolute Truth in Theravada Buddhism. Most of the time it is the conventional truth that is present in what we perceive. The disciples who are endowed with akarawathi saddha, have the developed wisdom to doubt, question and investigate the commonly translated Buddhist doctrine, to see this higher truth that is consistent with understanding of meaning (Artha), understanding of doctrine (Dharma), understanding of grammar (Nirukti) and understanding of eloquence (Pratibhaana).