I firmly believe that you live and learn, and if you don't learn from past mistakes, then you need to be drug out and shot.
There have been some friendships lost over this. That's the most difficult for me. I find it very uncomfortable to know that I was at one time close friends with someone, and because of jealousies and misunderstandings and so on, these friendships have dissolved.
Singing instrumental music is most important because, while you play an instrument, you are singing through the instrument... actually, you are singing inside.