Disclaimer: I am not Bulgarian; I know it only through an ex and her family. I learned some of the language but didn't get anywhere near fluency (it is easier than Russian though).

The Bulgarian national myth has an important chapter in the late 19c where Russia liberates their fellow Orthodox Slavs from the Ottoman yoke[0], paving the way for modern Bulgarian independence. This is a powerful historical memory for many Bulgarians, but is somewhat tempered by their experience of Soviet rule, and also by contemporary Russian territorial aggression. But in my experience you will still find a lot of older folks who instinctively sympathize with Russia for these historical reasons. I will defer to any actual Bulgarians here, though, who understand these matters much better than I ever will.

[0] https://en.wikipedia.org/wiki/Russo-Turkish_War_(1877%E2%80%...