I also want you to know that I take full accountability for my part in our relationship not being what it should up to this point. However, I don't take blame for an affair.
I would change that to say
I also want you to know that I take accountability for my part in our relationship not being what it should be. However, I don't take blame for infidelity - this is all his.
You may also want to add a comment about NOT wanting infidelity and the seedy lifestyle that comes with it around your children... Paints HIM and OW out as a creep while making you look like mature mother hen...
