It is a grace that you are bringing this question into the light rather than hiding it in shame. The honest answer is that the doubt you are describing — the struggle to feel God’s presence or to understand His ways in the midst of pain — is not a sin, but often the very place where God refines our trust.
Saint Alphonsus Liguori speaks directly to this fear that our spiritual darkness must be a punishment or a failure. He invites us to see this aridity not as abandonment, but as a hidden work of God:
"But you will say: If I knew that this desolation came from God, I would be content; but what afflicts and disturbs me is the fear that it comes through my own fault, and as a punishment for my lukewarmness. Well then; remove the lukewarmness, and use more diligence. But perhaps because you are in darkness, do you therefore wish to be troubled, to leave prayer, and thus double your evil? Let the aridity come as your punishment, as you say. But does not God send you this punishment? Accept it, then, as a punishment well deserved by you, and cling to the divine will. … But we must consider that aridity is not always a punishment, but sometimes a disposition of God for our greater profit, and to keep us in humility. … When God sends darkness and desolation, then He proves His true friends." [1]
This distinction is vital. A sin against faith would be a willful refusal to believe or a deliberate turning away from God. But what you are experiencing seems to be the painful *absence of feeling*, which the saints consistently describe as a trial permitted by God to purify our love, so that we seek Him for Himself rather than for the consolations He gives. Saint Alphonsso even suggests that persevering through this darkness is more valuable than praying with ease: "He who prays with sweetness does not do much. … God will grant a greater grace to him who perseveres in prayer with aridity than if he had prayed much with great sensible devotion." [1]
Your doubt, understood this way, is actually a form of clinging. It is the soul refusing to let go even when it cannot see. Fray Luis de Granada describes the strength that grows precisely in this silence:
"If you return to me and remain quiet in me, you shall be saved; in silence and hope shall your strength be (Is 30:15); and understand here by silence the quiet and interior repose of the soul in the midst of trials, which is an effect of hope, which banishes from it all disordered anxiety and distress through the favor it expects from divine mercy." [4]
The sin would lie only in abandoning the search or refusing to trust God’s goodness despite the darkness. But questioning, struggling, and lamenting *within* relationship to God is the language of the Psalms and the saints. You are not failing; you are being led deeper.
I wonder if this distinction between willful rejection and painful purification helps ease the burden you’ve been carrying?