WHEN I USE ?
Maybe this will help: "Pretty is like a little flower. Beautiful is like a sunset."
You are both erroneous in your elucidation in this manner. Pretty and beautiful are synonymous terms. Ofcoarse they differ in their origin and etymology but the idea which they are used to express are more or less the same. A flower can be pretty or beautiful, a diamond can be pretty or beautiful and a sunset can be both pretty and beatiful. However in terms of expressing admiration towardd a man or women it would be accurate to say sexy for female or handsome for male. Because obviously, these terms can only be applied to male or female seeing as how an inanimate thing cannot have a gender.
pretty often is used to women -" bonita " but you can say beautiful "linda".
Beautiful you can say about place you liked. " Roma is beautiful - Roma é bonita/ linda"
for men use Handsome and for women use Pretty.