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 & 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 & 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.'
If a person wishes to get married, the Buddha taught a suitable partner has the same life goals & 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.
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.
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.
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 & 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.
According to Bodhisattva, if you are unmarried then treat every boy and girl like your sibling. So, your question can be boiled down to, "Can siblings be friends?" to which I will answer, "Siblings are almost always friends!" The Buddha never spoke explicitly about this, though he mentioned that adultery is a sin and a hindrance to Nirvana- and anybody who commits his mind to such thoughts is also as much at fault as the one who actually commits the sin. There is no place for lust in friendship, so I think, yes. Boys and girls can be friends.
For the monastic, celibacy is a precept. For the lay follower planning to get married and become a householder, the consideration is much gentler, with a clear prohibition against illicit sexual conduct.
And what is the treasure of virtue? There is the case where a disciple of the noble ones abstains from taking life, abstains from stealing, abstains from illicit sexual conduct, abstains from lying, abstains from taking intoxicants that cause heedlessness. This, monks, is called the treasure of virtue (AN7.6 Thanissaro)
Notably, the lay path will be difficult: