Why can't you include your stepson? If it's because she won't let you, I'd make sure he understood that you love him and will welcome him any time.
I completely understand how sometimes you feel great, and then an hour later, you're wallowing, and wondering "wtf?" It's normal and natural. Be aware the healing and detaching is not linear, and has ebbs and flows. You will have missteps along the road. We all do. Don't dwell on them; the occasional mistake won't ruin your chances of reconciliation.
M:23 T:26 Me:53, Wife: 60 S:18 D:16 filed 7/16 W moved out 4/28/17