My girlfriend has said its over. I did something bad

Hi all, well here's my story.

Me and my girlfriend have/had been together for nearly 3 years. We have a great relationship, we are pretty aware that we are perfect for each other, we talk about everything, we like all the same stuff etc. We are really open, and one of things that has come from this is that we are both totally okay with each other watching porn. This was a little weird for me, because i've always had it in my head that its embarrassing, but i got used to it. eventually when we'd ask how our days were, 'watched porn for a bit' would come up quite often....its just normal to us

Anyway, i was on one pornsite and decided to make an account. i'd seen some videos that i'd liked and wanted to watch more, but they were on a protected profile, so to see them i had to be friends with this over user. So, i made a profile as a girl, so it'd be more likely this other user (listed as lesbian) would add me as a friend. At this point is were the bad bit happens. My profile attracted attention. i ignored it at first, but eventually thought, hey, i'll just pretend to be this person, why not talk to them. So it became that whenever i'd watch porn i'd also talk to random other users, exchanging sexy emails. I never told my gf about this, not so much because i thought i was cheating on her, but beacuse it was a totally pathetic, loser thing to do and i knew it.

However, she found out 2 days ago, i'd closed all my porn tabs, but left the chat window open. She is pretty furious, she says i've been cheating on her. I've tried explaining, it was nothing but porn to me, i only ever did it behind this cloak of anonymity and i'd never do it, as me. I've tried telling her, it was all just fantasy, like watching porn is, or it was like reading a sexy story, but helping it along too. I never wanted to do these things to these girls, it was all just something extra to add on to porn to make it better.

She however, can only see it as cheating. I've spent the last 2 days explaining, and telling her how sorry i am and letting her know i love her and i'd do anything to prove to her i never cared about these people (i closed the account immediatley). Shes having none of it though. Its cheating, end off and its over. Shes ended our relationship on facebook and deleted all profile pics involving me (so its all public), shes taken down all our pictures in the house, shes moved herself into the spare room (she is getting a bed off a friend at the weekend)

It seems now all i can do is give her time and hope she changes her mind, it seems like theres nothing more i can say

Any ideas?

Thanks