Can a girl & a boy be friends I didn't use to have much boys as friends but with time I made several boy friends from which some were really close. I want to know what has Lord Buddha chanted about a girl &amp; a boy being friends?  Will it be something bad when I get married?
If you are not married, the Buddha said to look at opposite sex friends like brother &amp; sister:


  'Come now, monks: with regard to women who are old enough to be your
  mother, establish the attitude you would have toward your mother. With
  regard to women who are old enough to be your sister, establish the
  attitude you'd have toward a sister. With regard to women who are
  young enough to be your daughter, establish the attitude you'd have
  toward a daughter.'
  
  SN 35.127


If a person wishes to get married, the Buddha taught a suitable partner has the same life goals &amp; attitudes; particularly living according the five precepts:


  Householders, if both husband and wife wish to see one another not only in this present time but also in the future, they should have
  the same faith, the same virtuous behavior, the same generosity and
  the same wisdom. Then they will see one another not only in this
  present time but also in the future.
  
  AN 4.55
  
  
  
  Householders, there are these four ways of living together. What four? A male wretch lives together with a female wretch; a male wretch lives together with a female goddess; a male god lives together with a female wretch; a male god lives together with a female goddess.
  
  AN 4.53 
  
  
  
  When both husband and wife are endowed with faith, charitable and self-controlled, living their lives righteously, addressing each other
  with pleasant words, Then many benefits accrue to them and they dwell
  at ease.
  
  AN 4.53 &amp; AN 4.55


If one or both people had many sexual partners before they get married and do not respect the precept of sexual fidelity then, as the Buddha taught above in AN 4.53 &amp; AN 4.55, their marriage will most likely (but not always) have problems. The Buddha particularly emphasised sexual misconduct should be avoided by and towards women, as follows:


  242. Unchastity is the taint in a woman. 
  
  242. In a woman, misconduct is an impurity.
  
  Dhammapada