My Girlfriend stole my FB password?

[Kevin]

Ok, so my girlfriend and me have been together for just over 1 year.
In March of this year she got really mad at me for writing to my ex girlfriend.
My ex called me teddy bear and BFF, and also told me I love you (meaning it as just a friend though)
So I did the same to here since I thought it would be no big deal, I don't talk much to her since she lives in Germany and I live in Holland.
We see each other once a year for 5 days and talk like once a week or less.

Then she came her and we went on a picture together , just a normal Friends kinda picture.
My Girlfriend who lives in America got mad, we got into a big fight.

I told my GF recently that it was stupid of me to call her those things but I didn't realize it would upset her (Everybody in this story is 17). OK so she told me she trusts me but not my EX.

I said OK, but told her many times that my ex and me won't do stuff cause there were never feelings. We broke up at age 14, most stuff we did was just play hide and seek etc. Never kissed etc.
Therefore I still think it is OK to hang out with her, we have never actually been in a real relationship, just a kids one.

My girlfriend gave me her FB password yesterday, so I just went on it and wrote on her wall how I love her. I know she has been talking with her cousin about this fight so I checked really quick. There I read how 1 day ago she confessed that she has my FB password and she read this in MY private message to my EX

I told my ex that no matter what I'll stay friends with her, since my girlfriend also wrote to her how she hates her !

Now she said to that cousin that she wants her out of my life and if she could help her do that.
She thinks that my EX is a threat while we barely even talk or meet up.

By the way my GF and my EX met up once and it was not to good. They only shook hands and later on she told me she hates her, my ex tries to make up with my GF though. My ex confessed through FB that she has 10% feelings for me but she also has a boyfriend for 2 years now, he knows that she called me those things and he doesn't matter at all, that's how some Dutch/German people are.

So I changed my password, what should I do, since my GF is lying to me about trusting me and how she doesn't mind!
I've told my Girlfriend plenty of times how I love her, and it's not the fact she's talking about the fight. She is lying about alot of stuff towards me !
And the last time me and my EX said those things was in March when the fight started, after that whe haven't met up in person (just once though but not without my GF being there) and still she's going on about it for 5 months already