This is really sad. I'm sorry to hear that your partner is not being honest with you... seemingly given the opportunity to be, she still feels the need to go behind your back even in front of your face!
When I got together with Mono we were texting fiends. I decided that if I couldn't read a text out loud, I would not respond until I was not around PN. It worked well. If I could say, "hey, Mono just said this" then I knew it was an okay time to text. We still operate that way and it works well. Somehow being able to pass on what others have said via text made all the difference to PN's feeling included and my feeling of respecting his need for my attention.
It sounds to me like she is either unaware or uncaring about what you think and feel. Very inconsiderate and disrespectful. It sounds like she and you might benefit from sitting down and hashing out some boundaries that work better. Trust is earned, not a given at this point I think and she needs to know HOW you will be able to trust her again. Maybe she is not clear that sneaking is not going to win your trust. I'm sure there are numerous boundaries you could present to her that address your needs. She likely has her own boundaries too. Asking her what they are might help.
I would wonder how much of her behaviour around texting and messaging is related to her addiction. Maybe she just can't help herself? I don't know. She has a lot to work on there and needs some serious counseling help I would think!
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