I omitted so much of the truth when I told my girlfriend I cheated on her.
Why would you lie about little aspects like that? She already knows that you cheated.
I don't feel bad about my behavior because I haven't really done anything wrong.
Cheating is wrong and it is good that you admitted to your girlfriend what you done. However, not telling the whole truth about what happened when you cheated isn't acceptable as your girlfriend still has the right to know what went on. You should be honest with your girlfriend and tell her everything what happened so that she can make a fully informed choice on whether to forgive you or move on.
Not saying the truth to someone who loves you is not bad.
I am going to have to disagree with you on this one. It is expected that you be completely honest about every thing that went on.