This is one thing that really pushes my buttons.   I had a brother who committed suicide when I was aged 13, and it was devastating.  But I am finding more and more these days, that youngsters (it is usually young people) will threaten suicide as a way of being manipulative.  Having suffered mental ill health myself I am sympathetic to anyone who genuinely feels suicidal, but saying you are in response to someone trying to set boundaries is in my opinion, despicable.

He got married because he can't have sex with his mini-wife.

Push the issue with him, and insist on couples' counseling.  If he wants to talk to her therapist, fine, but it's not a talk about whether or not boundaries will be set - it needs to be a talk about how to handle her if she threatens suicide after the boundaries are set, because the boundaries WILL be set.  A good therapist would not want her patient's parent to baby her and not set limits out of fear of threatening suicide.

"If you can't figure out how to enforce boundaries with SD, then I will have to find a way to enforce boundaries with you. I won't live in a home where you allow a teenager to rule the roost. I won't live with a man who will not parent his own child. If you want a wife, then you need to do a better job of being a husband and a father, and that means finding help and setting boundaries for SD because right now, you're failing on both fronts."

No need to argue. Tell him what the consequences of his actions will be. If he won't step up, then you're stepping out. If he is okay with you leaving, then as tog said, you're only there because he can't have sex with his daughter. All his other needs are being fulfilled, and you're only filling in the adult roles that a teenager can't play.

Except it's not a teenage girl but a 55 year old man who is my coworker . He has been texting for 9 months now suicidal he is. He had an extramarital affair two years ago with another coworker and they broke up over stepkids and money . Ha ha . So two years later he still loves her and wants her back and for nine months now I have been getting the worse text messages. He even text messages me a picture of a gun and said if anyone comes for him with handcuffs to baker act him someone is going to die. But he was definitely manipulating me saying if I could assist in getting them back together or message her for him that would be the only thing to save him. I never have and never intended to. I asked him to get therapy and help. So Thursday he said he was going to take his gloves off at work and electrocute himself in front of his apprentice . He is a lineman and I turned him in at work. So they force him to go to therapy Friday and Monday and he is saying he was never suicidal and that he was just trying to get me to help him to get her back. Ugh