This is a hard pill to swallow, but the truth is, no matter how long we are sober, no matter how much we rebuild, they don't want to be hurt again. They can't control what we do, so they do the next best thing. They mentally prepare for the next relapse, the next betrayal. If they never let their guard down and fully trust, it won't hurt as much, because they knew this was coming.
I can't be trusted because I am an alcoholic and always will be. Even if I get better, I can return to where I've been.
The only thing I can control is whether or not I drink.
I can't expect someone I've betrayed to trust me. I can ask for forgiveness and they can forgive me. But they won't trust me again, I took that from them.
New relationships? Blank slates? Those I can start out with a full tank of trust.. but I believe once it's gone, it's gone. Especially if someone is mature and intelligent. I won't work for their trust, I won't be getting it back.
Can you live with that, if that were the case with your wife?