He has limited MP. You can either find a way to drain his MP or once his MP ends he cannot revive more
I don't know why people seem to think this is hard. I've defeated all of the generals fairly easily, and Pride was the easiest one so far.
Just make sure you are at max level (which you should by by this point), and have full health/magic and potions when you go in. Arrange your skill points for max battle effectiveness, focusing especially on hp/mp regeneration and cooldown.
Then in combat, hit him with everything you have. Use the celestian form and its weapons whenever you can. Every time it ends you will be back at max health again. You can also use the sex attack time to let your used spells cool down.
Just keep hitting him and eventually he will stop regenerating and can be defeated.