How do I tell on my baby daddy?

So my daughters father has been persistent in trying to get me to sleep with him. It's been a whole damn year and more since I've been telling him no. He's actually married and his wife is pregnant and I want to tell her but the last time I told her she said I was jealous because he came back to her. We had our issues but now we talk in a friendly manner and it's been eating me up. He has asked for nudes, he told me if I ever tell her anything I'll regret the day I was born. Maybe I should tell her after she has her baby or none at all?

I do have proof, I have screenshots of the messages. But I showed her screenshots already and she didn't believe me. Maybe I should keep my mouth shut. I'll just do that.