I think everything that needs to be said has been said.

Having "been there done that got the T-shirt" (more than once fool that I am!) I firmly believe that although a leopard can change his spots it won't be with someone who he's already dumped on. It turns into too much of a routine.

No matter what you think or how detached you try to be you ARE going to start caring about him again, and get hurt, again.

So in short: don't get involved, move on!