re: I am TIRED AND FRUSTRATED with my friends wife flirting with me.

Yep, I made the mistake of telling a friend, without any evidence. She denied it, he got mad at me. That lasted for years, until he finally came around. We hung out with a group of people one night and he asked if I wanted to grab a beer and talk later that week. He died in a car accident before we got that talk.
Just stay out of it. Tell the girl to kick rocks, or, like you said, make sure you have solid evidence. Sometimes it’s just not worth getting involved anyway.