
Ditto to what 1 and 2 said - it’s a mix of him finding coping styles that work for him as well as the two of you finding ways where he can feel heard without triggering your anxiety. One thing in particular that has helped me with my doom spirals is to make a more conscious effort to care for those in my immediate vicinity and go out of my way to try to make a positive impact when I am capable of it.
“Doing what we can is going to look different for every person. For me, it is offering my friend a place to stay to get them away from their toxic family for a night or dragging my fellow depression inclined friends out to get food while I ask them questions about their interests and things they find joy in. Additionally, it may be donating to human rights organizations or local housing or dv shelters when you can.
That is to say, I think taking time to intentionally be part of the good in the world could potentially really help and has helped me. If there are specific triggers for you, maybe ask if those topics can be off limits. Journaling can be helpful, but in this case, maybe put barriers like timers or something in place so that it doesn't let it go out of control. It might help for him to try to find and join a community online of ppl who struggle w similar things who are also looking for support
At the very least, he could get some helpful suggestions on coping strategies that have worked for others or it could be another safe place for him to go so it doesn't overwhelm you. That isnt to say dont be there for him, but maybe it could help you to not be the only or main place that he is going.