Neelix traded with the Kazon.
They had a business relationship.
When he remeets them in the pilot, the Kazon are very angry with Neelix because he stole a lot of water off them during his last stay at their camp. It's a certainty that he met and "fell in love" with Kes during his last visit, or any of his previous visits. He might have stolen the water to buy mercenaries to rescue his "girlfriend" but he seemed to have lost what he had stolen by the time he met up with Janeway and used her resources instead. Although why he didn't steal the slave girl when he stole the water is a good question unless he had to pick one or the other and thought that stealing water was better for him long term than stealing a simple child slave girl who wouldn't even boink him... If Kes had put out on Ocampa, that means that Neelix would not have been around to great Janeway in the pilot because after he tried the milk for free why buy the cow, or he had chosen to steal the girl rather than all that water because she was a superb lover for a one year old and they both would have pissed off.
Kes later says that she left home shortly after her father died, which was also shortly after her first birthday... She celebrated her 2nd birthday in the episode Twisted that aired at the beginning of season 2, which was supposed to air at the end of the first season before life got difficult, but in either case she was a slave girl for the better part of 1/2 a year.