Not only does this phrase mean "need some drugs."

It's also used sexually. Many artist today uses this term in R&B songs to please another person; to make up for what that persons' partner can't do.

A person would get a fix if they haven't had good sex in awhile or just haven't had sex in a long time or haven't received the proper attention and care...therefore they seek someone else for a fix.

It's like a Boyfriend or Girlfriend #2. Pleasure P pretty much explains what a fix is in his song.

The person who needs a fix doesn't say they need it. The person who gives the fix usually offers because they can see the person is in need of one.
Remember with a fix there is no relationship involved, just relations.

A fix is most of the time free by a person who cares for the person they are fixing. Usually they know each other.