I have loved the circus ever since I was a child.
Is ever modifying since, was or loved.
The word ever is listed in most dictionaries as an adverb. I describe word functions as narrowly as possible, and the function of adverbs is: "an adverb modifies a verb, adjective or another adverb"
The most obvious/ closest modifying relation is to the word since, but that is a conjunction, and conflicts with my definition of the word function.