I'm a bit lonely, what are the best ways to make friends as a travel nurse?

Join a Meetup! There are Meetups for every activity or interest you can think of!

I hung out with co-workers and my roommate sometimes. Whenever I traveled to a new city I rented a room instead of a whole place to myself. My roommates have ended up being some of my dearest friends!

The Meet up app is great and I did that too. Also, ask some of your coworkers fun things to do in their town. Then invite them to join you! I found that they were really excited to show me around and made good friends that way.