RL, I don't know you personally, but I don't think you should be so critical of yourself when it comes to character flaws. What I do think is that you are a very gracious woman who is trying to keep the waters calm for her family since this Russian Tart is most likely going to become the step mother to your grown children. Also, I think you have a lot of compassion for people and that includes your oatmeal eating h. You know that something is very wrong w/him and that's where your heart is soft. There's nothing wrong w/the way you dealt w/the situation...but I wouldn't become their "therapist" for them.
As for living as friends, that could mean a lot of things. It could mean a marriage of convenience for her to get a green card, help w/the finances and taking care of the home, as well as taking care of him. I don't know if the authorities still do this, but long ago, they would check up on marriages such as this one coming up to see if they were real marriages or just a way to get the person into the country to live. I do think that they will remain married for a while and once she's established and knows that she won't be kicked out of the country, she'll find herself a real sugar daddy and leave your xh in the wind.
As for being too short...that's just an excuse to leave you. It's like the guy that left h is w because she purchased bagged salad. They can't justify why they are leaving, so they come up w/stupid stuff...but you can be rest assured, they don't usually hook up w/nice looking people and I have found that if they come up w/a character flaw for us, that flaw tends to show up in the affair partner. So, toss his comments aside...the flaws are in him.
I won't be the least bit surprised if the next thing they come up w/is suggesting that they move in w/you. I hope they don't suggest this, but I've seen this happen many years ago.
Continue to live your life to the fullest and only work on those things that you think need to be worked on.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.