Does "girlfriend" or "boyfriend" always indicate partnership?

Solution 1:

This is dependent on culture and context, but generally in North America, you do sometimes hear women referring to their platonic women friends as their girlfriends. You never hear men refer to their platonic male friends as boyfriends, however.

So girlfriend is a little broader than boyfriend, which does always refer to a romantic male companion.

(Whether the arrangement is exclusive really depends on a lot of other factors, however.)

Solution 2:

It depends on the gender and sexual orientation of the speaker.

A heterosexual woman might use "girlfriend" to refer to a close heterosexual female friend without meaning to imply any sort of romantic involvement. This usage tends to be confusing if the listeners are uncertain of the speaker's sexual orientation.

A heterosexual man or a lesbian would use "girlfriend" to mean a woman with whom s/he is romantically involved. It doesn't necessarily follow that the relationship is exclusive.

Certain gay men use "girlfriend" to refer to any of their close gay friends with whom they are not romantically involved. By contrast, the term for a romantic partner is "boyfriend." Again, it does not follow that the relationship is exclusive.

I suppose a lesbian might hypothetically use "boyfriend" to refer ironically to a straight or gay male with whom she has an affectionate but platonic relationship; however, I haven't actually heard any instances of this.

Solution 3:

Is this correct, or are there instances where girlfriend refers to just a "normal" friend that also happens to be female?

In addition to what other answers have said - my experience has been this depends a fair bit by age.

People who are younger do not use this as often in this context (probably because people who are young have a much higher chance of having a non-marriage relationship). But women who are older tend to be much more likely to use "girlfriend" in reference to female friends.