Not sure if it helps, but I just separated from H and I, too, feel awful. I think it's normal... at least that's what I'm telling myself. For me, the buildup to this point was so long in coming and I don't think there was really any other option for us, but going through the pain of the transition... watching someone else that you care about (I still do care about my H, sounds like you may too) hurt so much... knowing that you are taking steps to "break up the family", no matter how necessary it is... well, it's bound to be traumatic. I moved into a new house that doesn't feel like home yet. Having to tell people who know us and have been rooting for our marriage to work has been very hard. My kids seem to be doing OK but occasionally my girls (4yo) will say the most innocently heart-breaking things about living in two houses. It was step that I still feel needed to be taken, but damn if it isn't tearing me apart inside.
That said, it's only been 1 week since I moved. I do have times that I feel OK, and times that I feel VERY OK. I look around me and I realize how often I was making choices out of fear of what he would say about them rather than what I really wanted to do (both big decisions, and small things like items I buy at the grocery store). I feel like those times are going to get more and more frequent, and the painful moments will lessen as time goes on. People keep telling me, "You're going through a separation... you're SUPPOSED to be a bit of a mess right now." As much as I don't like feeling this way, I think they're right.
Hang in there.