All That She Wants is Another Baby by Ace of Base does not mean boyfriend, it means baby.

Some claim that in the song “All That She Wants” by Ace of Base “another baby” is synonymous with boyfriend (“Of course, baby means boyfriend”. *1).

Of course that is nonsense if you look at the lyrics to the song.

Look at:

She’s going to get you All that she wants is another baby
She’s gone tomorrow, boy.

How often is someone you would term of “boyfriend” “gone tomorrow”.

And look at:

“So if you are in sight and the day is right
She’s the hunter, you’re the fox
The gentle voice that talks to you
Won’t talk forever
It is a night for passion
But the morning means goodbye

So a one night stand is a “boyfriend”? Since when?

The meaning is what it says: she wants a baby, perhaps in order to collect welfare benefits in Sweden – which were quite generous at the time.

*1 https://books.google.com/books?id=kOdwBgAAQBAJ&pg=PT32#v=onepage&q&f=false