You're not gonna promise to each other that you will no disappoint one another, because at some point you will. What is important is you don't go away, you don't escape, you don't leave one another just because you were disappointed. That's the meaning of fidelity.
Yes to this in everything. This goes hand in hand with ways in which God provides for us: one of the gifts of the Holy Spirit is wisdom, which is the ability to judge the things of this world in light of the highest end of man-- contemplation of God. And if we keep this in mind as we buy less but buy well, we might just have more than we think when it comes to being generous with God and with others, especially the poor.