Welcome to the board, SW.
Borderline personalities are inherently unstable with difficulties establishing relationships. Even if your MLCer is playing the knight in shining armour, this will appeal to only one side of him. He will probably get exhasuted of the emotional changes (he has his own), the lies, the manipulation, and ultimately, the lack of real support for himself.
But this, for the time being, is his problem. He needs to realise this.
You need to look after yourself. Tell us more, and what your strategies are to protect yourself (and your children?)