"Express you love to your children generously and frequently. As much as possible, express to them also that they are loved by their other parent, the less visible one, the one who may have acted so very badly. It may seem difficult to defend your ex in this way, yet you are actually defending your child against a deeper and more difficult season of loss."
From Raising Great Kids on Your Own by David & Lisa Frisbie
This is tough, but worth doing.