Paarthurax participates in the killing of his own brother and king,Thats tough love and done for the greater good of the world to save it from Alduins tyranny.
Only that if what we are told is true and there is no reason to belive otherwise, tyranny is part of dragon nature, they all feel the need to be on the top, to be the one that rules them all, only reason other dragon serve Alduin is because he is more powerfull and they aren't stupid to risk fighting with him.
Personly I belive that what Paathuranax teaches isn't love, and he himself didn't really change that much.
If he lives then at the end of main story then he is taking control of large dragon group, and he will mostly like try to force them to follow the way of the voice, and after that it is possible that he will try to also forced other races to follow his way, as benelovent dictator of world.