I even know what she looks like: She's smaller and skinnier than I am, though I'm comforted to know that her head is disproportionately large and her face is quite flat and unremarkable; she's very pasty-looking and unhealthy--I don't think she gets out much--and she has tattoos all over her body. I don't know what he finds attractive in her--probably her mind, as there's no denying that she can do things I cannot--but I don't think she really puts out, so it's probably not the sex.
I know that she manipulates him: He buys her expensive gifts--moreso than he buys for me--and spends a lot of time maintaining her. He talks to her and spends time with her long into the night when he should be lying next to me. Even though she knows of me--we were friends before I married him--she lets him come and go whenever he pleases, flaunting their relationship to my very face. She claims that he can quit any time he wants, especially when my jealousy flares up, but he just tells her he'll be back, comes and talks to me, and then picks up with her where he left off.
Not knowing about her was better: Before we were married, I had no idea how much time they spent together. I thought they were just friends, that he needed her for help with homework or writing stories, that when we were married, things would be different....
I should've known better. I should've seen the signs: late-night when I'm awakened by his voice, I call out from the bedroom and ask if he's talking to me. He says, guiltily, no, and that I should go back to sleep and he'll be there soon. But I know he's talking to her, and I cry myself back to sleep.
Someday I'm going to put my fist through her face. Someday I'm going to stomp on her body so badly he'll never be able to touch it again. In the meantime, I'm going to delete her programs so she's merely a word-processing, solitaire-playing dinosaur like the first girlfriend my dad bought.