Yeah but you have to pretty much abandon your entire life to be with her. You have to abandon being prince-consort, warden-commander, bann of the alienage, and other things to be with her. And yes, you have to abandon your dog to be with Morrigan. As much as my character loves Morrigan, my canon warden thinks his duty is too important to be with her. Plus, I couldn't handle abandoning my loyal dog. What's going to happen to him if you go through the eluvian 

The Warden saved the world he deserves some peace, if he stays he will live a life in abject conditions (whenever another weird Darkspawn plagues the world with bizarre baby spiders), and then he will die in even worse conditions in the deep roads. With Morrigan he can at least have some peace and love with his family. That is what makes him leaving with Morrigan the good ending, people have been indoctrinated with the high fantasy trope of populism. Rarely in high fantasy do we see an individual's liberty and utility portrayed as being all that important, because if one looked from the top down (the populace, to the individual being sacrificed by the populace for the populace) one could say that the populace commits a kind of evil on the individual--as the individual is expected to sacrifice and to suffer, whether the individual wants to or not. I like that Gaider gave people the choice to break the trope with Witch Hunt. Edit: As for Dog, he was retired, and was being studded out because of all the Mabari that had been killed during the blight. I say he lived a fairly good life, and sired many pups.