You could show your firm attitude and make it clear that you have no intention of reconciling. Maybe avoid giving him any false hopes or ambiguous signals.
Well, one way could be for the character to seek support from friends and family. Another option is to move to a new place and start fresh, cutting off all contact with the ex-husband.
The protagonist could change their routine and environment to avoid encounters. Also, documenting any inappropriate behavior by the ex-husband can be useful for protection and as evidence if needed.
Well, you could try doing things he likes together to strengthen the bond. Also, showing appreciation and support for him can go a long way. Sometimes, small gestures of love and care can make a big difference.
One way could be to have heart-to-heart conversations regularly, listen to his perspective, and work on resolving any conflicts together. Surprising him with small gestures of love and support might also make a difference.