Suicidal thoughts?

I am new to this; therefore, I am really sorry if this topic has been already covered. However, I had no where else to go and talk about it and the things are just getting worse... 
My partner and I live together for over 3 months now, when we used to live separately, everything was amazing. Of course we had our little arguments, but I thought it was normal in a relationship. He used to tell me about his ADHD before, but I never really knew anything about it. As soon as problems appeared, I started to research all of the information about ADHD but I couldn't find anything about my problem. I am used to to partner saying awful things when he gets angry, because I know for a fine fact it is hard for him to control it. However, my problems are his suicidal thoughts. They can come anytime! I even once had to hold my partner tight so he wouldn't jump off the bridge and take the rope from around of his neck so he doesn't hang himself. Situation like this, really gets to me. They happen more frequently, and I am always trying to keep him calm. However, sometimes he just runs out of the house and I don't know where he goes. So I just sit there and cry, hoping that he gets home alive.

My main question is, is there a high possibility of him killing himself because of ADHD? Or does he do it to get my attention? Well, I wouldn't say to get my attention, but he might be just hopeless and that's the only thing that he thinks about. 

In addition, he had a really bad childhood, and when I say bad... I mean bad :( 

I am desperate... Many thanks....