It's definitely about the end of a relationship, however, I don't think "there's a pretty girl somewhere" means another girl. I think he loves her and doesn't want to lose her, but he knows he has to make her happy. "I sing 'I love you', so I'll say 'I hate you' tonight". He loves her... but, because he loves her so much, he'll do what's best for her, and end the war.
I'm going through the exact same thing right now and it's the worst feeling in the entire world.
It's definitely about the end of a relationship, however, I don't think "there's a pretty girl somewhere" means another girl. I think he loves her and doesn't want to lose her, but he knows he has to make her happy. "I sing 'I love you', so I'll say 'I hate you' tonight". He loves her... but, because he loves her so much, he'll do what's best for her, and end the war.
I'm going through the exact same thing right now and it's the worst feeling in the entire world.