Is there a way back?

[Piano]

It was your wife's responsibility to communicate problems in the marriage and work those issues out with you, not invite a 3rd person into the marriage.
She is probably being more negative about your M right now (they call it 'rewriting history') to justify her decision to be in contact with the OM.
It takes two to tango in a marriage, and your wife might have some reasonable grievances...but only accept responsibility for your chit, not hers.
Maybe you could restate your boundary about OM: " I have decided that I will not live in a sexless and loveless marriage and I certainly wont live in an open marriage. You're contact with OM has to stop or I will be considering my options". Others will help you more with this; be patient, hopefully one of the vets will be along soon.
Meanwhile read the Boundaries and Letting Them Go threads in Newcomers. Read,read, read, post here often and wait for advice before making sudden moves.