Answer:
It is about giving everything you have in a relationship and being cheated on in the meanwhile.
"On a bed of nails she makes me wait"
Waiting for someone to come back and thinking what might happen when the partner is gone; doubt.
"Through the storm we reach the shore, you give it all but I want more "
The relationship improves after the cheating happened, but there is doubt. Could it ever grow to the extend it was before?
I think that Bono got cheated on himself. In 1987 he said the song is about his relationship with the band and sometimes with the fans...