Yeah, writing things down, having a journal, etc. is very good for you. And yes, keeping her out of it is the right thing to do.
NOTE: The violation of your privacy snooping in such places she's doing is a very serious offense. If you doubt it, think how big a stink she would create if you snooped in her journal!
Obviously, pointing out the double standard won't do you any good... .but it might help you decide where to take a stand.
Oh, and I can't text or communicate with certain friends without telling her in advance, so she wants to make sure I'm not doing that. These are people I talked to about her behavior before I found out about BPD.
This is a problem.
I don't think that this restriction on you is at all reasonable, and I don't think it is something you should have agreed to. Not for friends who have heard 'bad' things about her. (For your former EA, this would seem more reasonable. So would "never contact her again"... .)
The problem is that you agreed to it.
If you just "change your mind" and don't tell her about it, she will be justifiably angry with you.
Better is to tell her that you've realized that this isn't a restriction you are willing to live with, and you will have enough privacy that you can call or text friends when you want to. And that you may share some or all of those conversations with her, but that is your choice, not her right.
Needless to say she won't be happy.
But you can enforce the boundary that you have that right and will use it.
Are you ready to?