Anxiety is a struggle for millions of people all around the world. I myself suffer from anxiety at varying levels of severity. Some days I can't so much as think straight, a result of how anxious I felt. This is what you should know if you love someone with anxiety.
They often hide their anxiety.
Anxiety is not seen as an attractive quality by many, so those with anxiety will often hide it away from the world. They do their best to conceal their anxiety and the causes of it.
Hiding it inevitably makes it worse.
The best thing you can do for someone with anxiety is to talk with them about it if they want to. You can't force the issue on them. If left to fester, anxiety can become worse issues.
Social situations are often the greatest trigger of anxiety.
Fearing what people think or being stuck around a bunch of people is typically the greatest trigger for people with anxiety. If you bring them into a public space, be aware of that trigger. They're most likely to be unnerved by disappointing other people.
They tend to be deep thinkers.
People with anxiety tend to think pretty deeply about things, so think deeply along with them. They're great problem-solvers, which is a benefit to being anxious. Help them solve problems in their lives.
They won't trust easily.
Once they do find themselves in a place where they can trust you, they trust you with all their heart.