"We needed Johnny as much as he needed the gang. And for the same reason"
She means that Johnny was an essential part of the gang and he needed them as they needed him to fulfill their objectives or they would not be accomplished.
Explanation:
This answer is the perfect example of a co-dependency relationship. First, because the gang required Johnny to subsist, while he needed them to survive. So they both were essential for each other, and they would not achieve their objective, as well as function as expected if the relationship was broken. Therefore, they both needed one from the other, Johnny the gang, and the gang Johnny. The gang organization would be damaged if he left, and he would feel incomplete without them.
