I’m surprised as well that this hasn’t been thought of before. I think that we were too focused on the new relationship being a “state” of adultery when in reality adultery is a sinful act, and the “state” referred to in the statement “state of adultery” is instead rather a state of public scandal; adultery isn’t a “state”, it’s an act. A state of scandal is not the same thing as an act of adultery, because the scandal can exist even if no act takes place, based on perception. But creating perception cannot, I think, be construed as a deliberate mortal sin in all cases.
If the Holy Father is saying that for the sake of family unity and children it is best for a couple in an irregular situation to remain together, and even to remain sexually active in order to reinforce stability, then that good can hardly be a perception of scandal and it seems to me it would be, in the modern context where serial divorce is a regular occurrence, in itself a sign of hope if the second union is long-term and stable.
I suspect then that he is separating the notion of a state of public scandal from the act of adultery. Again, adultery is an “act”, not a state. It is an act that consists of grave matter, but like other acts of grave matter, culpability is dependent on the other two factors for it to be mortal.
Interestingly we don’t speak of two unmarried people living together as living in a “state” of fornication. We euphemistically say they are “living in sin”; however the reality is that each and everyone of us is “living in sin” because “sin” isn’t just the act of shacking up, everyone is a sinner. The couple living together are committing acts of fornication (assuming neither of them was previously married). But the main sin is the act. People live together all the time for various reasons and should not automatically considered to be scandalous. In any case, I don’t think anyone is scandalized anymore by people living together.
So the Holy Father is saying basically that the act of adultery is just like any other sin, sexual or otherwise, that it is forgivable and may in some cases have mitigating factors that limit culpability. It’s no different than what the CCC says about masturbation. Some time ago in discussions during the two Synods, I brought up the possibility that this is the direction that the Holy Father may go in, without changing an iota of Catholic doctrine, but the “usual suspects” shot me down saying you cannot give absolution to someone in living in a “state of adultery”
I suppose he is also implying that due to the pervasiveness of marital failure and remarriage in our society it can no longer be construed as “public scandal” in most eyes, so the focus has shifted to the sinful acts themselves, reinforcing the stability of the union for the greater good (e.g. children), and working to the possibility of regularizing the irregular situation if possible, if not, maximizing the chances of creating a stable loving environment for the children.