It is a statement children say to comfort their egos; and yet, grown adults have scampered trying to recover from rejection and in their vast vocabulary and social prowess, when pride was the guide instead of God, the same words come to mind allowing the fall to be as painful as it should be.
Rejection can be a long walk back to the bar stool hearing the snickers behind one's back at the lame rap or waiting by the phone for that call one should get when the conversation seemed great and the physical attraction was electrifying. Sometimes it is expected but most of the time it isn't. And while we could (and have) moped in a small room listening to sad songs with the most fattening empty calorie food item that could be found, none of which will make you more accepted, more comforted, or more loved. The usual thing that the world does is a waste of time, money and the investment God put in you to do better because you know better.
Those revenge statements like, "I didn't love you anyway," come from bitterness. You are trying to hurt the person as much as his/her rejection has hurt you. No matter what you say, it will never hurt as much as those words will, when they (the words) come back to hurt you - again! God worked out the system that way. That's why Kingdom Living is paramount for us. Let the words of my mouth and meditation of my heart be acceptable in thy sight oh Lord, my Strength and my Redeemer (Psalm 19:14 KJV). "I didn't love you anyway" is completely derogatory of how we are to live. We know the word says how can you love God whom you have not seen and hate your brother whom you have seen (1 John 4:20 KJV)? Plus the basics by which Jesus tells us to hang all of the law and the prophets on. We must love our neighbor as we love ourselves (Matthew 22:37-40 KJV). With that one statement of not loving, you have given place to the enemy and now he can do his job: steal, kill, and destroy.
It is a blunt way of looking at the matter; that's why dating isn't for children and shouldn't be taken lightly. If the other party isn't interested, yeah it may not feel good initially but you will recover. So not to have a rerun of those feelings why not acknowledge Him in all of your ways so He can direct your path (Proverbs 3:6 KJV). Don't you see? It is because the blessings of the Lord maketh rich and He adds no sorrows to them (Proverbs 10:22 KJV) ; therefore hurtful words are a clear indication that he/she wasn't from the Lord anyway. Rejoice, again I say rejoice.