Understanding 2 Thes.2:3 in biblical context, is in two parts. Both parts must be interpreted correctly in order to understand the true prophetic fulfilment.
The KJV interprets the first part correctly with the words "a falling away".
As for the second part, one must discern by the Holy Spirit, (and not decipher by grammar) whether that man of sin is to be understood in the singular or in the plural.
2 Thes. 2:4
Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
We can safely conclude that "a falling away" is in reference to "and that man of sin", as being the subject that shall fall away.
So then, the words: "a falling away" implies that there are MANY people that shall fall away. But, if it be only ONE person that shall fall away, then the context doesn't support that conclusion, simply because the words "that man of sin" can be understood in the plural just as equally as it is understood in the singular.
By the Holy Spirit within me, I understand the words: "and that man of sin be revealed, the son of perdition" to be in the plural.
Why?? There are more than one person who is "the son of perdition [destruction]".
In fact, there are MANY who are the son of perdition that SHALL "fall away".
Yes, that is correct, there are MANY antichrists, NOT just only one! The reason for the many is because it is "that spirit of antichrist" that infects many. 1 John 4:3.
Did you know that in the KJV Bible, one will NOT find the words written: "THE Antichrist".