Advice how to navigate unhealthy co-parenting ?

My husband and I have a 1 year old. He has two daughters from a previous situationship. They never been together.

Even before I met him he has the same issue with her. The mother is issuing her kids to manipulate their dad.

She blocks him for 1-2-3, even 6months with no contact then unblock him, will authorize him to see the kids only to bring them to the dr appointment if he is in time good he gets reward he can see them for a full day but under her conditions: at her place, or around her place, most of the time with her. If he is late, back to square one he is blocked. If he is not showing up when she needs same, he is blocked.

I pushed him to go to court. But somehow he is incapable to set boundaries with her. Part of me understand because he wants to see his kids without too much tension or whatever we can call it. But the other part of me it’s thinking how long can he keep going like this.

The last 7 years has been the same pattern. He can be her puppy he still gets block at some point. And now we have a baby that never met his sisters!

Last weekend was one of the girl bday. Here again, puppy mode. He sacrifice our couple by going for a week end. I can accept having him spending the day with the mom for the sake of their daughter. But a whole bday week end. But let’s not even go in details because there are a lot of things enraging to say.

Now, he is an amazing dad for our baby. He is also my bestfriend. How can I help him in this situation. I’m not talking about founding a solution or forcing him or loving more. I’m talking how can I support him a way for him to be able to talk to me fully about the situation, without losing myself.