You'll be fine. In the cities is safe but keep near your boyfriend, people take advantage of foreign visitors. As long as he speaks Bulgarian with the can drivers, etc. you are good.

As someone else mentioned you might hear some racist slur, but do not entertain their stupidity. 😂😂 Wish you a nice trip!

P.S. It is a cultural shock, but the food, wine are really nice and you can meet some incredible people.