I haven't read all the thread OP, but I have read your posts in full, and would like to say that 'he doesn't want to be alone', as that will mean he has to cook his own meals, do his own washing, change his own bed, and generally have to grow up.
He's picked a woman with a child because he thinks he'll be able to move in with her, probably rent free, have sex whenever he wants it, and she'll cook, clean and look after him, as well as looking after his kids, when he gets bored with having to find something to do with them every week, when he'd rather be down the pub, and will generally take over the role that you have played for the whole time he was with you.
You say you are 34 and feel old. I left my first husband at 32, and am now in my 60's. In the intervening years I have lived a whole new life!! I have had a career, I have travelled, I have re-married, and while I am now disabled, I still have a WONDERFUL life, so please don't think that this is the end, it's just the beginning of a new life and a new you, and I promise you that you deserve so much more than he was ever capable of giving you, so whatever you do, don't give up, you life is just beginning!