Feng Shui: I rent an apartment where the front door and the back door are pretty much opposite of each other,?

put something in the middle that is bigger than the door - like a huge cabinet or a tall divider. front door and back door in a straight path usually mean that whatever you gain in life, like friends/ (life of people/family), money, properties, etc, are easily lost - loosing can mean from loosing money as expenses to loosing a friend or death in some cases.