I'm using the best actions, but it's still not working, I don't know what else to do
Viewing post in Secret ending
you have the 50 virility sword and one true cockring and plug set? You should, if using best moves depending on aura, be forced to heal ~3-4 times once reaching red but still win. The best potion you make at Valdo home will also give you significant boosts that make the fight easier after you reach red once. I'll see if I can record an example later.
Edit: I highly recommend getting focus enchantment on something if getting the hits every time is part of the problem. I think I also used the heal 5 each turn.