Perhaps, that would depend on the person and circumstances, is it a fair weather friend or someone who came through in the time of need. 

If a former "friend" has attacked you then i would not advise any further close relationship with such a person. Life is too precious to spend it on people who care not about you, especially when they are close to you. As the good book says, don't spill the pearls before the swine.

Another old proverb says, "stupid are not those who make mistakes but the ones who do not learn from them." Sure, be friendly, that is a healthy and positive attitude, however trust your better judgement. Sometimes friends need a friendly reminder about the real care that bonds the friendship together.

The folk wisdom confirms, "show me your friend and i will tell you who you are" or "you are judged by a company you keep."

However, that said, fire is not fought with fire. Hate only begets hate. There are laws, of peace and of wars, private and public, of the spirit and soul, of the earth, of the whole universe. Action/Reaction, Cause and Effect, reap what thou sow, Do onto others what thou wilt be done onto thee in West Christian or Don't do to others what you don't want to be done to yourself in East Chinese traditions, etc...

"Ralph Singh told the story of Gobind Sadan, his Sikh 
community in Syracuse, New York. Its place of worship, 
a large farmhouse, had been destroyed by an ignorant 
and hateful act of arson after the attacks of September 11. 
But the community responded from a place of love, with 
a statement and prayer of forgiveness. "If we show hatred 
to those who act against us . . . we will only perpetuate the 
cycle of violence that exists in the world. By forgiving our 
enemies we have the opportunity to create peace.""*

_\|/_ namaste _\|/_ 

peace.

http://www.virgin.com/richard-branson/lifes-too-short-for-enemies

*http://global-forum.org/goldenrule.html