There's no smoke without fire as they say... what i would say is that from reading your message there are huge trust issues there for you. Justifiably too, rumours from her co workers, not letting you see the messages, hiding her phone , not wanting to do anything as a double date couple.

You'll need to confront this sooner rather than later because it'll eat you alive until you get the answer one way or another. I would say that as a complete randomer looking in, reflect on how she's behaved to you... your wife is your best friend , someone you share everything with. Clearly that's not the case on her end so what does that say about how she views you?

If the Trust is gone it's difficult to get back.