1 Corinthians 7: 39The wife is bound by the law as long as her husband liveth; but if her husband be dead, she is at liberty to be married to whom she will; only in the Lord. 40But she is happier if she so abide, after my judgment: and I think also that I have the Spirit of God.

Paul ends here telling us that marriage is meant for life and is meant to be permanent. If one of the spouses dies he says it is OK to marry again but only to another believer.  Because marriage was meant to be permanent the disciples thought it better not to marry. In really God say not to be unequally yoked which means to marry or remarry it should be to a believer. Paul ends saying it is better if one becomes single after being married it is better to remain that way so they will have more time to concentrate on their devotion to  God. He even with a touch of sarcasm says he believes he got this word straight form the Holy Spirit. Also a lot times it is better just to remember the good memories of the the one you loved for so long rather than look for another.