Could this also be "I had asked him because he hadn't spoken with you."?
No, that would be, “Gli avevo chiesto perché non ti aveva parlato.”
I understand that perche' plus the subjunctive means "in order that." Something like "I had asked him so that he wouldn't speak to you."
Thanks - that's useful to know but I don't see where the "wouldn't" comes from in your translation.
Nothing deep. I was trying to make sense of an obscure sentence. You can ask a person not to speak to someone in the future, but you can't ask him not to have spoken to someone.