How is one supposed to be compassionate and 100% free of suffering while others are suffering? How is this possible besides if one simply doesn't mind if others are suffering? 

But if one truly doesn't mind whether others are suffering or not isn't that a lack of compassion? Is one supposed to let go of compassion regarding others? 

Even if there is nothing that one can do to help the other being, even if one is doing one's best, wouldn't the desire to end all suffering for all sentient beings still be present and therefore suffering still existing in one before that goal has been achieved?  

I don't see how it is possible for a being to be compassionate and free of suffering while still knowing that others are suffering. 

Is it supernatural? Does it transcend reason?
How is this possible besides if one simply doesn't mind if others are suffering?


Its not a matter of not caring. It is a matter of each person must end their own suffering. 


  Even if there is nothing that one can do to help the other being


Correct. Well-spoken!!!


  I don't see how it is possible for a being to be compassionate and free of suffering while still knowing that others are suffering.


The above is a contradiction. When it is realised there is nothing one can do to help the other being; the mind let's go; and ends its suffering. However, the mind, free from suffering, is always willing to compassionately help another person help themself. 


  Is it supernatural? Does it transcend reason?


Sorry. Please don't feel criticized but, in my opinion, your post does not accord with reason. When it is realised there is nothing one can do to help the other being, this giving up of desire or absence of hope is Nibbana. 


  The phrase 'absence of hope' may be used in regard to the attainment of arahantship, but it's not the resignation of the foolish and lazy,
  it's a different matter altogether. It is the absence of hope of one
  who with true wisdom sees that there is nothing in this or any world
  that one should wish to have or be. Truly nothing is worth having or
  being at any time or at any place.
  
  Heartwood from the Bo Tree