Hi Philip, I think you'll love the city! I moved to Poland, Wrocław five years ago and enjoy it here a lot.
I'm a straight white guy, and don't attract "unwanted" attention (fortunately Wrocław is also super vegan-friendly), and it is indeed a very open-minded city just as Bartek noted above. But you should know that Poland as a whole still isn't the most tolerant country out there, which isn't a surprise to you probably. My friends of color may be hearing remarks and catching odd looks outside of the city center. Often times it's sincere / unconscious curiosity, no bad thoughts attached, but it's nothing like a big US city or nearby Berlin when no one gives a thing about how you look or what you do.
This is my speculation based on observations after living here: I don't think you will have much issues, and if you work in an international company, with a healthy collective, you won't need to hide your relationship. Some Poles working with you may find it weird, but won't say anything. Publicly, just be careful. People won't care really, but one incident due to stupidity of someone may spoil your experience in Wrocław and I personally would not want that to happen 
In the very center of the old town there is now an LGBT-friendly cafe (and a pretty good one, just slightly overpriced), so things are definitely getting better in that regard.
