It does not remove youā¦
Yes we are* obliged *to confess all mortal sins in number and in kind (and circumstances that change the sinā¦like it was your brother you murdered).
And if we
forget one or to say the numberā¦so long as we are sorry (via the normal requirements for confession) and not hiding the sinā¦it can be *absolved *indirectly along with the other mortal sinsā¦or if one did not have any other mortal sinsā¦the āat least one confessed with contrition etc venial sinā (one of course has contrition for all ones mortal sinsā¦and one would have confessed it etc had they known itā¦).
But one is obliged to confess that mortal sin that was forgotten (not concealed!) in the next confession (I would do it soon so one does not forget itā¦but it perhaps could be argued that one ought to do it like within the year if one does not go frequently) when once one has remembered it.
It is
not that one then all of a sudden leaves a state of graceā¦one only does that by a new mortal sinā¦(which though can happen if one then saysā¦I am not going to confess that mortal sin even though I know I am obliged toā¦with full knowledge and complete consentā¦but that is hopefully not going to happenā¦)
(and one of course go to Holy Communion ā¦one does not have to wait til one confesses the honestly forgotten mortal sin in confession)
Venial sins can be forgiven in many waysā¦though yes confession of them (at least some) is very recommendedā¦