Op I don't know how old your kids are, but I have been in your situation for 10 years, only difference is mine has 3 step children, whose needs he places in front of his own two. Chooses not to play any part in their lives apart from taking them for dinner twice a month, yet is a great and hands on stepdad.
I think how you deal with it has to reflect the personality of the child, ie with a not-so-sensetive child you can be more breezy and make light of it. But I have come to understand that nothing I say or do can protect them against the hurt & rejection.
When they reach their teens they start to look at their parents more critically and form their own opinions. What I have done is to try and strengthen other areas of their lives to compensate, eg a strong social life, great stepdad, loving grandparents- and of course me.
Where I come unstuck though, is that I know I ask too much of their stepdad to 'compensate' for what they miss in their dad, and that really is too much of an ask.
Hopefully, although we would never wish this situation on our children, they will grow up to be more sensitive and make better, more loving parents themselves.