2nd Thessalonians 2....

" 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;

4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God."

The falling away comes before the day of the Lord in the verse....I dont think its saying that the falling away needs to come before man-of-Lawlessness comes.