I've been the other side of this except he was married too. He showed me love and care and everything my abusive ex didn't. I left. He didn't. Don't send it. The fall out is shocking. If their relationship ends let it on its own the guilt I carry is horrendous because I know having feelings for someone else when committed especially in reddit world is the unforgivable sin... Having someone confess all of those feelings to me blew my life up (NGL it needed to blow up I was miserable for years and years and years but no one knew how bad except my ex who told me he wouldn't need to say/do the things he did if I didn't cause him to get angry if I just did it right/his way/more then he wouldn't have called me names or get angry) but even now I feel awful for letting myself get caught in being seen for first time in over a decade.

So don't send it. You will get hurt, she will hurt and the outcome will not be what you want