I always felt that one of the most important tasks as a single mother after breakup was to make sure I never exposed my children to negative talk about their father.
I feel the same goes for a stepfather who filled the shoes of a father for a longer period of time.
Even if the man was an a-hole, you keep your own anger, bitterness, disappointment and whatnot to yourself. And make sure the kid doesn't overhear you ranting when on the phone or with friends.
This will help the child keep a more positive view of love, relationships, the (step)father. If you don't, you ingrain them with fear and anger concerning love relationships and partners.
Also talk about the good things and good memories. Very important for the kid, and for you too. A breakup doesn't mean the time spent together suddenly was worthless.
Look at what you have learnt from it, that helps to move on.

The part about you yourself is time. Time to heal, get over it. And that takes time :)
Count on a year to find your own feet and more time after that to really heal the heart. Doesn't mean you feel crap all that time, not at all. Just that after about a year, year and a half you suddenly realize you feel "you" again.