Re: How can I explain to my girlfriend that I did homosexual things when I was younger?
Why did you feel you had to tell her? As I said in my last post, what you did back when you were 11, isn't uncommon. Did you even read what I wrote to you?
It sounds like you're a teen still living at home. Am I right? If so, tell your parents that you would like to get some counseling. You could tell them that you have a lot on your mind that you need to sort out. If they won't help you, then talk to your guidance counselor at school.
To be honest, from what you've written, this relationship isn't healthy for either of you. You need to work on what is troubling you---and quite frankly, so does she need to work on her issues.
I hope that you do work on your issues. As I pointed out to you, it's a good first step that you are aware of your poor behavior towards her. You need to work on changing this---and you will need help to do so.
Here is my suggestion (and you may not like it)---you should seriously consider breaking up. IMO, it would be the best thing for both of you. Then don't get into another relationship until you've worked through your issues.
Again, good luck and please get going!