And what will he say tomorrow?

any idiot knows fornication is not a good thing

My point is that Francis says it's not a mortal sin, so his exhortation to confess mortal sin rings a bit hollow.

Receiving Holy Communion is “the most radical call to holiness” that any person can encounter, the Bishop of Shrewsbury will say in a pastoral letter this coming weekend.
Bishop Mark Davies will warn them against viewing the Blessed Sacrament in terms of “secular inclusiveness” as this diminishes its true significance to little more than a “token of our hospitality”.
Catholics must realise instead that through the Real Presence, the gift of Christ’s Body and Blood is the means to become the saint each of us is called to be.
Holy Communion restores strength to the faithful, breaks disordered attachments, separates Catholics from sin and helps them root their whole lives in Christ, the bishop will say.
Catholics must also repent of any mortal sin or lifestyle which contradicts their calling as Christians before they can receive Communion, Bishop Davies will remind his diocese.
“We see why we can never approach Holy Communion casually, still less if we have not confessed and repented of any mortal sin or of a lifestyle in contradiction with our Christian calling,” the bishop will say.
“The Apostle Paul urged the first Christians to examine themselves carefully before receiving Holy Communion because anyone who did so in an unworthy state would, he said, be ‘guilty of profaning the body and blood of the Lord’.
“The Church calls us to frequent Holy Communion, prepared by the Sacrament of Penance and Reconciliation so that we might become holy, might become saints. The Second Vatican Council urged us to ‘frequent’ both these two Sacraments eagerly and devoutly as the path to holiness.”
“Let us ask ourselves how we seek to receive Him with the deepest reverence and love, and how we spend the precious moments after receiving Holy Communion,” he will add.

http://catholicherald.co.uk/news/2018/04/02/receive-communion-lifestyle/

Where does he explicitly say that fornication is not a mortal sin?

Understand what he's doing in Amoris Laetitia.  He's saying that something which is objectively mortal sin can now be venial sin if someone discerns it away ... i.e. can rationalize it to himself.

Understand what he's doing in Amoris Laetitia.  He's saying that something which is objectively mortal sin can now be venial sin if someone discerns it away ... i.e. can rationalize it to himself.

In order for a sin to be mortal three things are required;
grave matter ( fornication is grave matter)
free consent ( that would exclude rape)
knowledge (It is understandable that there are some people who do not understand the gravity of this sin. this lack of comprehension could mitigate the culpability for this act. That would be true even prior to Vatican II.)    

In his most recent apostolic exhortation, Gaudete et Exsultate, Pope Francis warns that the devil is not a myth but a “personal being who assails us”
 
 http://www.catholicherald.co.uk/news/201...al-claims/

and he gets us to believe all kinds of falehoods
but as the song says "We decide which is right and which is an illusion" (moody blues)

The devil is a great liar. Don’t talk to him or even get close. He tries to seduce and like a chained rabid dog, if you caress him, he bites.
According to Vatican News, Pope Francis stressed this during his daily morning Mass at Casa Santa Marta as he reflected on the figure of the devil who is not dead, but “has already been condemned” as said in today’s Gospel of today’s Liturgy, taken from John (Jn 16: 5-11).
Fighting and overcoming temptations, the Pope reminded, requires being on guard, praying and fasting.
We must be attentive to the devil, the Pontiff underscored, as he “seduces us, knows how to touch our vanity, curiosity and we buy everything,” that is “we fall into temptation” and suffer “a dangerous defeat.”
Beware, the Pope warned, of the devil’s seduction.
“The devil is a seducer,” Francis reminded, saying, he “knows what words to tell us” and this is dangerous as “we like to be seduced.”
“He has this ability; this ability to seduce. This is why it is so difficult to understand that he is a loser, because he presents himself with great power, promises you many things, brings you gifts – beautiful, well wrapped – -‘Oh, how nice!’ – but you do not know what’s inside – ‘But, the card outside is beautiful.’ The package seduces us without letting us see what’s inside. He can present his proposals to our vanity, to our curiosity.”
His light, Francis said, is dazzling, but it vanishes.
The devil who ‘is very dangerous,’ the Pope admitted, presents himself with all his power, yet “his proposals are all lies.” “We, fools,” he said, “believe.” Stressing the devil “is the great liar, the father of lies,” the Pope noted, “He can speak well,” “is able to sing to deceive.”
“He is a loser but moves like a winner,” whose light is dazzling, “like a firework” but does not last and fades, whereas the Lord’s is “mild but permanent.”
“If I know that spiritually if I approach that thought, if I approach that desire, if I go that way or the other, I am approaching the angry and chained dog. Please do not do it. ‘I have a big wound …’ – ‘Who did it?’ – ‘The dog’ – ‘But he was chained?’ – ‘Oh yes, I went to give him a caress’ – ‘But you are sought. ‘It’s like this: never approach …. Let him chained there.”
Do not converse with the devil
Finally, we must be careful not to dialogue with the devil as Eve did.  Jesus does not dialogue in the desert, but rather responds with the Word of God. He hunts the demons, sometimes he asks for his name but does not make a dialogue with them. The Pope’s exhortation is therefore very clear: “With the devil he does not dialogue, because he wins us, he is smarter than us”.
Noting the devil disguises himself, the Pope said: “He is a convict, he is a loser, he is chained and about to die, but he is capable of making massacres. And we must pray, do penance, do not approach, do not talk to him. And in the end, go to the mother, like children. When the children are afraid, they go to the mother: ‘Mom, mom … I’m scared!’ When they have dreams … they go to their mothers.
“Go to the Madonna; she guards us. And the Fathers of the Church, especially the Russian mystics, say: in the time of spiritual turmoil, take refuge under the mantle of the great Mother of God. Go to the Mother. May she help us in this fight against the defeated, against the chained dog to win it.”
Pope Francis concluded, urging us always to seek refuge in the Mother of God.

https://zenit.org/articles/popes-morning-homily-dont-dialogue-with-devil-keep-a-good-distance/

I hope that everyone here seeks refuge in the Mother of God.