Have you told her about the thoughts that go through your head and that you know they aren't rational? It sounds like a great deal of paranoia to me... how stressful!

Can you make yourself a list of all the great things about your wife that let you know that she wouldn't cheat on you? Then when she's out the door you can read over it and remind yourself that you're being silly. I tend to think everyone's mad at me and/or doesn't like me at all, so I'm consistently reminding myself in my head of all the things that they have done/said that is proof that I'm just imagining that they don't like me.