*hugs* it is so hard, just take it day by day! My ex moved his next girlfriend in 3 days after I left a 6 year relationship. It really hurt, but now, 3 years on, I am so grateful to her for being stupid, as she saved me from being stupid, as I have no doubt I would have returned. My life is so much better now without him and the constant stress of him!
Just hold your son close, and reach out as needed for support.