quetesh is the black sheep (doesen't the MC have a history with sheep? ) so perhaps feritility was her origniaal domain but thanks to her relationship with nergal she focused on sex and pleasure. But the last 20 years gave her time to think.
Possibly... so hypertheotical plot idea based on what we know in 3... 2... 1!
What if Lord of Light (LoL from now on) has a siscon & hated Qetesh with Nergal, who was driving her further from fetrility & closer to downright sexual desire. LoL trigger Goblin Wars by orchestrating Nergal catching Qetesh with MC's father. Near the end of the war MC is born & "blessed" by Nergal to be their Chosen One, in their plan to fully stomp out Qetesh using her bastard child as an unwitting final steak to the heart in her destruction.
The end game could play something like this: the Nergalites & Qeteshians build their strength with allies, artifacts & knowladge in prep for war with each other. MC manages to get Qetesh & Nergal to stop fighting & LoL gets mad, attacking both sides in a final bid to make things go his way. MC then leads the now combined forces of Qetesh & Nergal against the LoL's forces (Purifiers & Angels) in order to defeat his main Priest (a ape-like figure). With his defeat the LoL is now in the same position he put Qetesh in.
That way we can unite the w factions & still have a big bad for the end game. What better being to be the big bad than the one who is the anti-thesis of BOTH factions.