Hello and welcome, Will.
I don't expect that you'll get much discussion of "Catholic" virtues per se, because there aren't many Catholics here. There are, however, many Christians.
Faith is the assurance of things not seen (Hebrews 11:1), while fidelity is enduring commitment to a person, entity, or cause. In terms of Christian beliefs, faith (in God and in Jesus Christ) is central. I don't know that I have ever heard fidelity discussed in a Christian context, other than in terms of honouring one's wedding vows.