I saw this on a page here and it was very helpful. It describes my goal:
"Very often when we say we want to help a loved one with Borderline Personality Disorder, we mean that we want the loved one to stop being a burden to the family, and to better attend to our own needs and expectations.
Not good for us. If a loved one enters therapy or alters their behavior mostly to please us or out of fear that we will abandon them, are we helping them or are we being selfish and emotionally manipulating? If so, this is not the best starting point for healing and recovery - and even if successful in getting someone in - will likely see pushback in the form of passive aggressiveness and resentments."
I have spent over four years trying to coax my child's father away from his drug addictions, away from his self-hate/angry/depression/paranoias, and attempting to support him financially and emotionally to get himself into treatment. After years of this, the only result was... .I was drained and resentful, and he was exactly the same as he was when I first met him. Except, now, rather than finding me to be his "idealized savior"- I became the new person to blame. He then promptly found another new friend to idealize (until, of course, that person "abandoned" him aka stepped away bc any healthy person would step away, really). The entire experience taught me something that was hard to accept and swallow but that is CRUCIAL to my future happiness and the stability of my child's life.
My partner will not change.
If he does change, it will be due to him and not due to me. Any attempts to help or change my partner, no matter how well meaning, are reflections of my own weaknesses (a need to be a savior to someone maybe, a need to fix things, a fear of being alone and a single parent, etc.). The more I address my own weaknesses and accept that this man is a drug addict and severely mentally ill, but still seems like a caring individual who loves their child (even through this filter of selfish self absorption which BPD symptoms really are) the better off I am.
For example, parenting alone has been excruciating recently. I juggle work and all the bills and managing a household and my future pursuits and also a toddler on my own. They were sick this week so it was especially hard to juggle work and parenting. I feel resentment that I do not have a partner to help me. If I express that resentment, it will backfire. There is no reason to express the resentment because my child's father cannot change or be what I need. Expressing anger will just cause them to react with anger in response and thereby make my job even harder.
Instead, sending a nice note saying I look forward to our future trip in which I will bring our child to see their father in a supervised setting, will be a positive step. It will likely result in a positive feeling in my child's father and also a positive interaction between us. This does not mean I am accepting that I *deserve* to do everything myself, or that I think it is fair- it isn't. It simply means I accept life for what it is, and make choices with the choices I am given. I am making the choice that is best for me and for my daughter, and that is to post about my anger on this forum instead of again obsessing over finding therapists or trying to figure out how in the world I can bring my child's father to sanity in order to have an actually helpful partner.

It simply won't happen. I am better off making a plan to help myself. I will begin by once again reaching out for babysitters.
I have also begun by simply posting here. I already feel much better, actually- far less angry- and more focused on myself and my needs.