How do you cope/deal with other people's anxiety disorders?

I'm trying to advise a close friend, but I don't think PTSD and anxiety are exactly the same. For example, I withdraw and isolate rather than push my feelings on others (then I write about it for all the world to see...). There are similarities and I think a lot of the skills I learned in Emotional Regulation and DBT would be helpful, but I'm not doctor and shouldn't make assumptions about other mental health things.

What are good treatments for severe anxiety?

How do anxious people break their cycles?

How do you help your friend deal with their spouse's anxiety?

What steps can you do as the non-anxious person in this relationship?