When trying to decide between careers, it may be helpful to think about choosing the career that would be the most fulfilling and rewarding to you. Talking to someone in the fields you are thinking about, may give you insight into what the jobs are like on a day to day basis. Creating a pros and cons list for each job, may help you see the benefits of each job.
Ultimately, I encourage you to choose a job that you'd do if money weren't an issue and something that will make you happy in the long run.
You have gotten some great advice here. I have struggled with trying to figure out what I wanted to do. The challenge here is that both of them are not just something that you can really know what it is about until you try it or observe it in real life. I would say if you can job shadow someone in the job that you want, that is one great way to get more information on what the career involves. Another way to compare jobs is to actually go to college. You can take classes without declaring a major, so you can take a deep dive into topics that may interest you. Also another consideration is making thinking about how you want to do each career. So with nursing, do you have a specialty you want to pursue? For example, my sister-in-law is a labor and delivery nurse. I also know some people who are nurses in doctor's offices, which is more general. The same would be with whatever art that you like - do you want to be a singer? And lastly, is there a way for you to merge your two loves? There are jobs that merge medicine and arts - such as Art Therapy. In many ways, most jobs are not all or nothing.
When I was growing up, job options seemed so black and white to me: doctor, lawyer, nurse, teacher, etc. What I didn't realize until I entered the workforce as an adult is that it's not black and white at all--it's a rainbow with infinite color choices! Instead of feeling like you have to choose either art or nursing, look for careers where your two passions intersect or overlap. For example, you could become an art therapist where you can use art to heal people. Or what about working as a nurse in a residential facility or special school for sick/disabled people where you can do art classes with them? Keep an open mind; there are so many careers out there that you have yet to discover. And there will be jobs you learn about in the future that don't even exist yet!
In the meantime, use Google to search for careers where your two interests overlap, then work backward to figure out what education and training you will need. You may find that it makes more sense to major in one field and then use your elective classes (or a minor) to study the other.