The usage of "friend" friend and friend is quite simple.
When the question is posed as such, a friend is "just a friend" (a platonic relationship). When someone is a "friend" friend (commonly said with extra emphasis on the first word and often with quotation fingers), the implication is that there is something more going on. While it can sometimes be interpreted to mean a budding relation (amorous, i.e. "just dating"), it more often refers to having relations (carnal, i.e. "friends with benefits") with them.
Because the quote also includes boyfriend we effectively get the following interpretation about the relationship:
- boyfriend - amorous
- "friend" friend - carnal
- friend - platonic
Had the boyfriend option not been included, the "friend" friend option would be slightly ambiguous.