I assume zawjuki is correct. Isn't it?
Yes! Furthermore, if we follow Standard, it will be:
As an adverbial place, خلفَ is always "khalfa".
Does "is behind you" mean, "is standing in space behind you", or does it mean, "he supports you"?
In this sentence, it means "is standing in space behind you"
Both, I think
Can it be خلفک زوجک یا روزا؟
What is this structure called in arabic? It Mudhafa?