I understand the Ex-OW arrangements now. I'd be hesitant about a friendship with the OP as well. Just complicates things unnecessarily, and there are many other fish in the sea for friendships for both OW and you. You're not obliged to serve her needs, Ioavva.
Thank you for reminding me of your Ds' ages. That is busy! You posted elsewhere that they tend to idolize you a bit since you are the non-custodial parent. I find S5 doing that with me as well, and think it also has to do with our being the same gender. I 'get' him better than W does at some times/on some issues because of it, I think.