I think you guys are missing a very important element of this song. Yes, it's about happiness, and yes it's about "perfect" love, but it's about striving for both of those things in an unhappy, imperfect relationship.
It sounds like the relationship she is in is not how it used to be. They hurt each other, and she wants it to get back to how it used to be. She loves him so much that her "mind see-saws" but it's to the point that she feels that "I love you when I forget about me." She can only love him if she forgets how awful he makes her feel sometimes and vice versa.
She just wants it to be a happy, healthy relationship again.
I think you guys are missing a very important element of this song. Yes, it's about happiness, and yes it's about "perfect" love, but it's about striving for both of those things in an unhappy, imperfect relationship. It sounds like the relationship she is in is not how it used to be. They hurt each other, and she wants it to get back to how it used to be. She loves him so much that her "mind see-saws" but it's to the point that she feels that "I love you when I forget about me." She can only love him if she forgets how awful he makes her feel sometimes and vice versa. She just wants it to be a happy, healthy relationship again.