Term or phrase for something that changes one's life (for the better) dramatically
Solution 1:
Boon
Something that is very helpful and improves the quality of life.
--Cambridge Dictionary
You could modify it with a word such as tremendous, or major to stress the tremendous and dramatic impact of the boon.
Behind this flawed creation of technology, however, was hiding an epochal momentum of my life.
Your sentence is a little awkward (epochal momentum, aside), I would rewrite like so:
Behind this flawed creation of technology, however, was what was to become a major boon for my life.