Welcome Dadlife:I'm sorry for what you are going through with your Partner. Are either of you currently in therapy? How are things going with the children? Are you currently able to visit them?
You say there is always a lot of volatility. Can you give some examples of some to the behavior problems? If you are able to share some details, we can help lead you to some specific lessons. In the meantime, the two set of lessons below can be helpful for you to look over. I'm sure something will jump out at you as being helpful.
If you click on the link below, it will take you to some information to help with decision making:
DECISION MAKING GUIDELINESThis link will take you to some lessons focused on Improving a Relationship
LESSONS FOR THE IMPROVING BOARD