ולא יכול יוסף להתאפק, up until now Joseph had practiced restraint in every one of his actions and words to the brothers. As we know from 43,31 “he restrained himself and ordered the meal to be served.”

He cried over them, etc. 

After the brothers observed Joseph crying over them they were able to respond to him and they said to him whatever was on their minds. After all, everything that Joseph had said to them up to that point might have been designed only to alleviate the brothers' feeling ashamed of their conduct. It was only after he kissed them and wept over the years they had been separate that the brothers recognized Joseph's truly good character and that he was a true brother that they were able to speak to him naturally. Whereas Joseph's original burst of weeping could have been attributed to his reunion with Benjamin, the latest burst of weeping definitely concerned his reunion with all of them.

See how precious is the sign and groan (the krekhtz) of a Jewish person. It provides wholeness in place of the lack. For through the breath, which is the ruach of life, the world was created. As is written (Psalms 104:30), "You will send your ruach--they will be created; You renew the face of the earth." This (ruach) is also the vital force of human life. This is because a person's breath is their life-force. As is written (Genesis 7:22) "All in whose nostrils was a nishmat (breath of) ruach-of-life." Regarding this the wise men said, "To the extent breath is lacking, so is life." And sighing is the extention of the breath. It corresponds to erekh apayim (patience)--i.e. extending ruach. Therefore, when a person sighs over the lack and extends his ruach, he draws ruach-of-life to that which he is lacking. For the lack is in essence a departure of the ruach-of-life. Therefore, through the sigh, the lack is made whole.