We have a terminological gap in referring to relationships. An example is the notion of boyfriend (or girlfriend). Basically, as we use this term in the USA, it refers to a person of the opposite sex in which there is a romantic component. But what about those relationships in which two people happen to be of opposite sexes, but there is mutually no romantic relationship?
Some people refer to a "friend date" -- one in which a man and a woman (or bay and girl) go out together and do date-like activities, but in which there is no romantic or sexual component. This would be something that you might do with your opposite sex friend.
It's interesting that there is the slang expression "friend with benefits" to refer to a friend that one engages in sex with; and even "friend with minor benefits'; i.e. -- non-coital sex. But there is nothing to refer to a relationship that is strictly platonic.
Maybe Platonic friends?