go back a long way:很久以前就认识了,相识已久
例如:She and I go back a long way. I've known her since I was in elementary school.(我们是多年的朋友了。我在小学时就认识她了。)
It's great to have friends that you go back a long way with. You always know that you can depend on them.(有个老朋友真好。你知道你能永远信赖他们。)