Liz -I think it's really smart of you to go ahead with the separation after all that you've been through to this point. If he is sincere, it will show & your relationship will strengthen despite the separation. If not, you will be able to see it more clearly & already have the physical distance you need to minimize your interaction.
I think it's also a great show of your inner strength for your DS to see that even if you aren't sure of where this is leading, even if you are hesitant or just completely scared to your core about this change - you have faith that doing what it right for YOU TWO is the right thing to do no matter how hard that road may be.
Just making this decision to separate has been agonizing for you - all of us here have watched you struggle with this for a while. Sending you lots of STRENGTH today & always!!!