You can't make him set boundaries.  Unless and until he is sick and tired of the crazy, he is going to continue letting her push.  The fact that he was willing to agree not to see anyone else due to threats that were likely baseless is not a good sign.  They would make him lose his house?  Really?  Obviously the answer is to say good bye to his daughter and hang up the phone when he discovers that she is also on the line and when she says "you won't be bothered with us anymore" (drama queen much?) to say "OK crazy lady - I'll talk to you when you can act like an adult."  But if he is still afraid of her and not confident in his ability to enforce court orders for custody then she will be able to sense it and will play with him like a cat plays with a mouse.  It is up to you how patient you want to be.

No. You are right. It was a typical BM move to try to guilt daddy into explaining to the girl why they couldn’t be a happy family. He was right to tell BM to keep those conversations away for the kid. There will be a time to tell her but it damn sure isn’t at five years old via late night phone calls. It sounds as if the BM you deal with us the game playing type so the best way to “win” is to refuse to play. Don’t answer unexpected calls, don’t respond to text that aren’t about the skid, communicate through email/text, never agree to change pick up/drop off times or swap holidays aka always go with the custody order and understand that any favor you ask of her gives her slight power to cause problems in the future. It’s a two way street so you can’t get mad at BM for not following the court order if y’all are also asking for little changes here and there to accommodate y’all. 

I think that biomom got sd worked up and then used it as an opportunity to manipulate your boyfriend into feeling guilty for not being with her. This seems to be common... parent putting their own desires and ego above the emotional needs of their child.

unfortunately one lesson I have learned as a SM is that there is very little to nothing you can do besides be there for your DH when things get rough for him.

With the threats the Mom makes it can go one of 2 ways.... either she will find someone new herself and drop it, or will get over the jealousy and the relationship and move past this behaviour or she will intensify it and follow through on her threats.

Botrom line there is really nothing YOU or your boyfriend can do to control it... you are pretty much along for the ride. He can try Court, but that doesn’t always do much good either.

Focus on your relationship and providing a great life on that front for you and your boyfriend and the rest will fall where it does. 

When someone breeds with a person who is mentally ill, they can expect that their life is going to be hellish for at least the next eighteen years. There will be cascading issues resulting from the exe's behavior and the child will be affected by this. Additionally, there is a genetic component to bipolar dsoorder, meaning the child has a predisposition to it as well. For years to come, your boyfriend will likely be playing Wack a Mole trying to deal with his disordered ex and the damage she inflicts on their daughter. 

You should think critically about whether you want to be collateral damage in someone else's life. If you decide to stay, buckle in for a looong haul. Educate yourself on mental illness and father's rights, and pick up a second or third job because your boyfriend will likely be in and out of court quite often. Get used to being financially strapped, coming last, and the feelings of dread, waiting for the other shoe to drop, anxiety, and depression. Peace and calm will be elusive, and forget about things getting better when your bf's daughter turns eighteen because she'll either be damaged by her mom, showing signs of her own mental illness, or both.

I wrote a blog post on mental illness in steplife several years ago, and you're welcome to check that out. Also read posts in the Mentally Unfit Bio Parents forum. Since this site tends to draw people from unhappy/dysfunctional step situations, it's not at all surprising that mental illness is a component in many members' lives. You're not married to this man, and his daughter is still young so the worst is yet to come. Please learn everything you can and take care of you.