You may want to check out Blended Family on the bump.
I have two SSs (18 and 16). Their mom has pretty much stepped out at this point. Occaisional phone calls/texts. No visits, etc.
I try to be a very consistent, fair, "mom" presence in their lives.
My situation is different than yours. I am their primary caregiver. They have dinners with me each night, I handle the rewards and the punishments, I give dating advice, sex talks, etc Unfortunately due to the economy, DH has had to take a major backseat with our family.