I am sorry for your grief.
While your wife is a fantastic person for being understanding and open to you exploring your bisexuality, I think there is work to be done in coming to terms with the idea that people are not interchangeable. In your situation, it's particularly obvious, because there is no way she can provide what a man provides. You mourning your loss is no reflection on her at all. I mean if you have two kids and lose one, you don't say, "oh well, I've got another."
And I have experienced much of what your wife is experiencing. I was part of a MFF triad - a married couple plus me. The triad didn't fly. I left. A year later, they separated and started divorce proceedings, and the husband and I eventually reconnected. But our reconnection in no way ameliorated his grief over the loss of the marriage with his wife. Why? People are not interchangeable. Doesn't matter how great we get along, I am not her.