I'm so sorry to hear your news, but it sounds like you're being sensible by calling it a day now while you and your wife are still friends. As you seem to get on so well with her, why not discuss your concerns with her? obviously don't go straight in there saying about different blokes etc, but you could say that its a concern for you that, at some point in the future, a new man will come into her life, and therefore the life of your son. I'm sure she'll have every empathy for you, and may even be feeling the same way about a new woman in your life. Are you planning on living close to the flat? If so, how about you collect him from school once or twice a week? as you're friends, i'm sure you can arrange something that you all go to the flat or maybe out for tea once a week on top of your normal times to see him. Speak to her frankly and honestly about it and try to agree as much as you can between you, as once the Solicitors are involved, you may feel as though things are taken out of your hands. I wish you the very best with everything xx