Hi thoughtsbecomethings
This might not be what you want to hear but… I have an on old school friend (married with kids) who had this happen to him and his wife. The wife was sent photos of her husband and his OW having sex :( :( Apparently, the wife was sitting waiting for him when he got home from work, with the photos on the table. It was their daughter's birthday party night. :( He'd been having an affair with a much younger woman who he had made various promises to leave his wife for. When the younger woman finally realised that he wouldn't, she decided to send the wife the photos… The wife went absolutely berserk at him, and rightly so.
So it may actually be a good sign (?? - if any of this can be classed as good) i.e. this woman hasn't got what she wanted, so thinks she'll mess up what you have together. On the other hand, its a case of do you want him now after all this?
The 'stalking' thing is a classic male get out. Sorry. My cheating ex said that about them all!
I would contact the OW and ask her for her version of events. Stay calm, and don't apportion blame (even if you want to) whilst you're getting all the information out of her - dates, times etc; and then compare them against any texts, emails, diary entries etc you have from those same times - to see if there stories add up i.e. he texted you to say he was working late on so and so night, she says they went out on the same night. Then calmly confront him with the facts.
I'm really sorry this has happened. There are some real shites out there (male and female.) xxx