No, you aren't an idiot when it comes to R's. You're confused and hurt and struggling, just likt the rest of us.
RE: your stepson -- have you thought about contacting him to see if he'd like to go do something with you and your sons? After all, you are the adult in that R. If R's are left up to teenagers, nothing would ever happen.
If you are so inclined to include a letter to your xw with the check, I would encourage you to keep it light, funny, short, engaging. Remember -- NO R TALK! You don't even have to talk about her. Share a joke you've heard recently, or mention something fun you've done, but not with too many details. Light and fun. Period.
So, what have you done for yourself lately?
And since you seem to think nothing you've tried has worked, I would ask you to consider some 180's. What are things that did not work during your M that you could do a 180 on with your xw?
You don't even have to talk about her. Share a joke you've heard recently, or mention something fun you've done, but not with too many details. Light and fun. Period. 