I cheated on my girlfriend
What made you decide to cheat on her?
I thought it was a necessary step in order to improve my relationship.
Cheating on your partner is never right. You will not strengthen your relationship by being unfaithful; you will just prove to your partner that you are untrustworthy and selfish. You should apologize to your girlfriend and try to earn her trust back.
I think she should just accept it. It's not like she cares about me anyway.
Whether or not you think she cares about you, you shouldn't cheat on your partner. You are in a relationship for a reason. If it is making you unhappy you should discuss it with her.