I know that but you can't stop the power of love. You can try to fight it but it's too powerful. I believe even tho he dropped her and called her that he did it put of anger for himself because he lost his true love & it was his fault. Even now in the episodes you see Zeref in he looks pained and it makes me feel bad for him. Yes he may be the ultimate dark wizard but look at all he had to go through. Wouldn't that change who you are if you had to go through all that? If you lost a family member and had the power to bring them back.. would you? He was blinded by the love that he had for his brother to see the mistakes and wrongs that he was doing. Love is a powerful yet dangerous emotion.