They were madly in love once, but the relationship probably soured after all the fighting and quarrels. And the song kinda reassures the girl that he's always hers to keep, no matter how he may have failed. He does want the girl to see past their trials and rediscover the love they once shared before the fighting set in. That's why "the best thing about tonight's that we're not fighting", and so "tonight will be the night that I will fall for you; over again".