As I see it, you have a choice of three: 1) you can do nothing and not rock the boat, yet continue to suffer in silence 2) you can try to avoid the person outright, or make contact as brief as you can, maybe ask to change departments or change hour gym or wherever this is happening, or 3) you can ask the person when they have a few minutes to talk, and address this 800 pound gorilla in the room head on, truthfully, tactfully, civilly, and fairly.
Maybe the person isn't aware of whatever it is that troubles you. Maybe you are being overly sensitive about something they can't help or of which they are not aware.
Or, sadly, a permanent physical separation may be necessary, whatever that entails. If it is conduct that is illegal, or hostile or intimidating, you can report it and have whatever powers that be figure out a solution, hopefully involving input from you both.
Very good luck to you. I hope everything works out.