Its political marriage so i don't fault him for that. The whole continent is split between the North, the South... and... I forgot whatever they called the middle one. Each of this have a "princess" or some other woman of high standing that is married to him "to ensure peace" (and gain political power, depending on who you ask).
First of all, the prince needs an heir. So he has to marry someone. Since Paullianna is rumored to be barren, she is out. As Emperor, he can only marry people of high standing cause thats how society works. Marrying one would piss off the other two regions so he had to take more than one. He settled for 3 so that its "fair". Each princess gets 2 nights with him and he gets one night to himself. Can't blame him since it is part of his duty as an Emperor. The fact that he doesn't do sh1t for Paulianna despite being in love with her on the other hand is his bad point.