Oh Eagle, this is all such hard stuff to navigate.
I too have been in a similar situation and have grappled with the same dilemma with regards to the children. Mine are younger than yours, however I don't think that changes the approach.
Some of what has carried me through my situation has been the thought that I will not feel this way forever. DnJ's 'feelings are fleeting' (ha! read his last post about the empty coffee bin distracting him from his dark thoughts about J leaving 4 years ago today).
So first, in this very moment in time, do nothing. Because anything you do or say to the children will be fueled by your feelings and not your rational brain. You need to process this information on your own before you can process it out loud with your boys.
Then, ask yourself if telling the boys: 'is it true? Is it kind? Is it necessary?' If the answer in your heart is 'no' to any of these questions, then don't say anything and keep waiting for a while.
I have some truths that I live by with regards to raising my children:
1. I don't believe in lying. To children or to adults. 2. I believe that children will ask the questions they are ready for the answers to.
If you hold similar values, then you don't say anything until the children ask directly, because they if they don't want to know, they will not ask. And when/if they do ask, listen very carefully to how they word their question. Your answer should only be in response to what they ask, nothing more. Maybe they say 'Mama, I think Dad has an OW' then you would ask them 'what makes you think that?' and listen to what they say. Or 'do you think Dad has an OW?' you might say 'I am not 100% sure.' <= Our instinct here is to continue on with '...but I think so' and that part can be dropped.
Be comfortable with silences and be comfortable with not having an answer right away (you were SO good to say 'I am not able to answer this right now' with S17-- it is always OK for any human to say to another person 'I need to think about that, I will get back to you').
In summary: 1. Don't offer information that is not directly asked for 2. Answer questions in increments, do not offer more than they are asking for 3. Attempt to protect your children for your children's sake, if you can do so without lying
I am sure that voices wiser than mine will chime in with different advice and I look forward to reading them. In the meantime, give yourself a big hug and lots of grace as you get through the next few days with this information.