I suspect that you're right, he doesn't know what he wants. More to the point, what he wants changes from moment to moment along with his emotions. It's truly an exhausting and confusing position for the non to be in. Anyone experiencing what you wrote about would be left that way.
I'm glad that he ran away when you yelled at him and that he didn't hurt you. Do you have a safety plan in place in case things escalate again?
I tend to believe that your son is right, you should give him some time and space to bring his emotions back to neutral. It typically takes people who exhibit BPD traits longer to reach emotional equilibrium than it does others.
In the mean time, you can use the space to work on you. You noted some financial concerns that you can start to work on to protect yourself in the future.
This sentence stood out to me:
I know though when he is raging he can't stop until he finishes.
While that may or may not be true, it doesn't mean that you have to be around or take part in his raging. Have you taken a look at the
3 Minute Lesson on Ending Conflict? Before the two of you can make things better, you have to stop making things worse. In your post, you mentioned that you recognize some habitual things that you do that probably only make things worse.
It's good that you recognize these things! It means that you can change your own behaviors and thus change the dynamics of the relationship. Don't expect a drastic change instantly, and don't get discouraged if things seem to get worse before they get better. Anticipate that this is going to happen and be prepared for it.