Just saw your thread. We have a similar sitch. My H is 34, has an online other woman (OOW) who is nearly 50, married unhappily, with a grown daughter. He thinks I don't know about her.
I have a D, age 6. I believe my H is in a MLC, also said he's not "in love" with me, hasn't been happy for a while, all that jazz. If you want to read all the gory details, my thread is titled "Dealing with a Depressed Husband" in the Newcomers forum.
Get the "Divorce Remedy" book; it definitely helps. And do as other have said: Be kind your spouse (tell yourself that he is suffering and having internal conflicts) and put your focus on you and your son. Do things for you -- read, do a hobby, paint your nails, exercise. Play your little boy, have fun with him.
And come here for support.
M 39 H 34 D 6 M almost 8 years T 11 years Bomb: 6/5/08