So you want to log in and heart images, but you forgot your username. That happens to all of us, don't worry.
Do you remember the link to your heart page? If you do, you know your username. That's because your username is the last part of your heart's link (http://weheartit.com/your_username).
If you don't remember that you'll need to reset your password. If you reset your password you'll receive an email with your username and a new password. You'll be able to log in and change your password back to what it was before.
Read our article on Recovering a forgotten password