emotional rollercoaster
Term first used by R&B singer Vivian Green in her 2002 single "Emotional Rollercoaster" from the album "A Love Story". It is used to describe the varied emotions that a person (usually someone you're in a relationship with) has you feeling for them. For example, your girlfriend cheats on you with your best friend. As much as you hate her for cheating, you can't help but keep loving her because she has you so sprung. 
2.) When your emotions go up and down like a rollercoaster. For example, you keep slipping in between happiness and sadness.


Vivian Green: "Boy i'm so tired of you making love to me, and then disappearing so suddenly. 'Round and 'round it goes.
And I'm so tired of you pacifying me with promises you know that you'll never keep......I'm on an emotional rollercoaster loving you ain't nothing healthy; loving you was never good for me."