I've been using my ex's email to sign up for spam sites for years
Why would you use your ex's email?
I'm too lazy to delete the her mail id.
Even though she's your ex you should not do something that will cause her any problem. You use your email for signing up sites so her inbox must be flooded with spams so you should stop it.
No problem. I think I won't use her mail id for signing up things.
I'm glad that you have reconsidered doing this! Stopping to use her email is the right thing to do.