Is he who assists in a sin—such as one who provides an address for a place that sells alcohol, then repents before that man buys the alcohol—guilty of the sin of drinking alcohol or not?

Guiding people who commit sins to the locations where those sins are committed is a form of assistance to them in their wrongdoing, and it is forbidden, as Allah Almighty says: "And cooperate not in sin and aggression." However, Allah accepts the repentance of a servant from any sin, and the one who repents from a sin is like one who has no sin, and the lingering effect of his sin after repentance does not harm him. It is incumbent upon the one who guided to the sin to strive to prevent the person guided from committing it, if that is possible for him.