Don't be to hard on yourself. You apologized, whether he accepted it or not. You did your part. He made his bed and now he has to lie in it with OW, with finances, with SIL.
Maybe it would have been better not to send the email but it was done. Just put it behind you. Next time you feel the urge, type the email but DON'T send it. You can tell him how you feel without the fallout then.:)
