I don't mean to fuck up your Christmas

I'm really tired of saying "I'm sorry" to Lacey. It's not that she's demanding it, or anything like that. It's that I keep fucking things up. Today was the worst. I didn't face punch her, or anything of the sorts, but I'm sure I upset her as much as if I had.
She got a text message from her roommate, Staley. I read it to her, thinking nothing of it. At the end, it said "your monitor arrived." Initially, I didn't think anything of it, but Lacey was quite visibly upset that I'd read it. She left the room and I went after her. She was crying a lot.
Long story short: she apparently bought me a computer monitor for Christmas and had kept it quite the secret. Accidentally, Staley managed to tell me. It was such a huge accident, but it still happened. I keep seeming to unintentionally upset her. I really, REALLY need to try harder not to upset her. I love her so much and she means so much to me.
I will quit doing this. It's just so wrong to her that I keep accidentally fucking up. Therefore I will try even harder to prevent shit like this from happening.