Oh the great falling away has all ready start you can see that a few differnt places in the Bible. For example:

3 John 9-10 - I wrote to the church, but Diotrephes, who loves to have the preeminence among them, does not receive us. 10 Therefore, if I come, I will call to mind his deeds which he does, prating against us with malicious words. And not content with that, he himself does not receive the brethren, and forbids those who wish to, putting them out of the church.

Look John is telling us that brethren is being put out of the church, so while John himself was still alive we know that it was happening and happening enough that he had to write about it!

A couple of questions, and not just aimed at you! You said something like what is the heart of God, that reminded me of when people say that the "love God". I like to ask, ok you love God but what does that mean and how do you show God love? I normally get some vague generic answer but for me I turn to the Bible...

1 John 5:1-3 - Whoever believes that Jesus is the Christ is born of God, and everyone who loves Him who begot also loves him who is begotten of Him. 2 By this we know that we love the children of God, when we love God and keep His commandments. 3 For this is the love of God, that we keep His commandments. And His commandments are not burdensome.

You also mentioned lawlessness...oh man that is everywhere these days. Many people thinking they know better than the Creator, well those that believe in Him in the first place. The simple definition of lawlessness is one that breaks the law...right? We know that the lawless one is the working of Satan (2 Thessalonians 2:9) Ok, what do we know about Satan, loaded question I suppose. But what I am asking is that in Genesis 2:16-17 God said to Adam "And the Lord God commanded the man, saying, “Of every tree of the garden you may freely eat; 17 but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.” Now the serpant comes along in Genesis 3 and is already questioning what God said. Verse 1 "Has God indeed said, ‘You shall not eat of every tree of the garden?” Then the women added to what was told to Adam in verse 2 and 3. So what happened here? Satan questioned God's word, then deceived "man" to add to what God said and all this caused them to sin against God. Circling back around to...ok but how does the Bible define sin?

1 John 3:4 - Whoever commits sin also commits lawlessness, and sin is lawlessness.

All this means is the man of lawlessness is the one who disregards the commandments of God and breaks them. How do we know what the commandments are, we have to look to "the faith which was once for all delivered to the saints."(Jude 1:3) Paul also tells us:

Romans 7:7 - What shall we say then? Is the law sin? Certainly not! On the contrary, I would not have known sin except through the law. For I would not have known covetousness unless the law had said, “You shall not covet.”
Romans 3:31 - Do we then make void the law through faith? Certainly not! On the contrary, we establish the law.

Keep seeking my friend and I pray that this is edifing to not only you but for anyone else they may read it!