Watching someone you love struggle with anxiety can leave partners feeling helpless, especially when reassurance does not seem to make much difference. It is common to want to fix the problem quickly, even when that is not really possible.
Often the most useful thing a partner can do is simply stay steady and present, rather than trying to talk the anxious thoughts away. Asking what would actually help, rather than assuming, tends to work better than well meant advice.
Couples counselling can be useful here too, giving both partners a space to talk about how anxiety is affecting the relationship, not just the person experiencing it.