Note that the word 'therefore' (stressed on the first syllable) has a final e. Confusingly there is also a word 'therefor', stressed on the second syllable', that means 'for that thing' *- almost exactly the opposite, in some contexts:
'A, therefore B' -> B happened because of A, or 'B. The reason therefor was A.'
To avoid confusion, people have let the second one fall out of use. (Online Etymology Dictionary )
PS This mirrors all the other 'there + preposition' words, such as thereat, therein, thereafter, thereupon... (all of which are fairly obscure, and can sensibly be ignored for most exams ;-))
Ok, thanks. I take it that it IS correct to say 'Therefore, this is why I chose to live my life this way' then.