STTC, I don't know if this will help you, but it helped me. I instituted a "no talking about DS in any context except therapy" rule for one month (and I considered this site and one other one as part of therapy). I let my boyfriend and my friends know that I didn't want them to ask me about how I was doing with the situation, or bring him up in any way, and I wasn't allowed to mention him either. The purpose of it was to get some practice in living like the person I was before I was a mother, and also to make myself aware of how much effort and focus I had put on DS instead of on myself and my own life.
I had to deliberately look at my life and say, "ok, what was I like before I had DS? What were my interests? What did I talk about? What makes me happy?" And then I slowly started to, again deliberately, focus on those things every time I got sad or angry about DS. It takes time, and I had to be careful to allow myself to grieve and be sad when I needed to but with a firm time limit each time. (Like, I could wallow and be sad, but only for an hour, and then I had to go run errands or call a friend, or clean something.)
It was hard. But, I'm over 4 months into it, and I've found it to be a really useful way to keep myself from obsessing about DS. I talk about him sometimes now, but very little, and very factually (describing actual events, but briefly, and with a specific point in mind - not just to relive them).