I can best explain by using a simple example.
"This smartphone costs less than $100" is a simple statement of fact.
"This smartphone costs even less than $100" communicates two ideas at the same time:
a) This smartphone costs less than $100, and
b) $100 is a very low price.
The smartphone is cheaper than cheap.
In your example, "even" strengthens the statement by saying more than "before I realized X." It isn't just before I realized X. It's before I began to realize X.