You and your ex-spouse never got along well, but it's come to a point where you both know that you have to change or risk harming your relationship with your child. You are involved in a high-conflict relationship when it comes to your child, but there is help.
It can be hard to co-parent when there are many things you disagree on. One thing you can do to combat this issue is to agree to go to mediation. Talk to the mediator, learn what other couples do and air out the issues you have. Allow a third party to keep things calm while you talk them through.
If that doesn't work, a better option is to go through therapy together. Family therapy is wonderful because it allows a psychologist or psychiatrist to get to know you and what does and doesn't cause conflicts between you. By encouraging you to change certain behaviors you have that cause conflict and vice-versa, many parents are better able to handle interactions with their ex-spouses and work toward better relationships all around.
High-conflict relationships have a negative effect on children. Children are often put in the middle of these conflicts, and that can cause extreme stress. As parents, you both have to know that this isn't an acceptable situation for your child. The good news is that you both have the ability to overcome your differences and agree to raise your child based on set terms and arrangements. By reducing conflicts, you'll begin to see your relationships recovering and be able to support your child more effectively.