Well, without any further details (including the state), you behave as a parent when it is your parenting time. You develop an amicable relationship with your child's father so that you can co-parent as rational adults. Barring any major issues that render him *legally* unfit, you remember that he is the man you chose to father the child, and you deal with that reality. Your child deserves both parents in his/her life.
What were the custody and visitation orders entered at the time of the divorce? You question is vague but you should remember that they are your (plural) children and not your (single) children. You get to raise them together unless and until a court rules otherwise that their other parent is unfit.
Please begin reading threads on this forum about what you should/would/could expect from co-parenting arrangements. Also, please post specific questions; the crystal ball is in the shop for repairs. Although the volunteers are talented and helpful, they cannot read minds.