Well, that sounds like quite the problem…
I’m not really an expert on kids. Never have been. I’m good at entertaining them in the short-term but anything longer and I’m useless.
First off, I think you should know why your son wants to kill your soulmate. I’m sure you do, so just keep that in mind with whatever you do next.
You say your son is psychopathic and yeah, I guess that he sounds like he probably is. So you should think very hard about whether your relationship with your crazy son or your relationship with your soulmate is more important. Anything you do will depend on your decision there.
If you want to keep your soulmate in your life, which you probably do considering that’s what you call him, then you need to ask his feelings on the matter. Can he put up with your son? Does he want to?
I’m not saying kick your son out of your life. But I am saying that maybe you need to consider some alternative methods of dealing with him. Sometimes medication can help even people out. Maybe it can help your son to feel a little kinder toward your soulmate.
I’ve never dealt with a problem like this before. But both of these people are important to you. Maybe try to get them in a stable environment to talk their problems out before doing anything else. Knowing more about the situation will help fix it.