I'm sure finding the note wasn't fun - it's hard to have such a concrete reminder no matter how much you were already aware of and dealing with an issue like that. Good on you for not confronting him, though.
I appreciate your attitude that OW isn't really the problem. This took a long time (too long!) for me to realise, and it caused a lot of damage in the meantime. I hope that not focusing on the OW gives you more space to be able to deal with the real issues in a way that produces some positive changes.
M - 34 H - 36 Together 10 years Married 4 years BD - March, 2014