kdt's post makes me think of another point...
It's kind of like asking, "How can I learn Quantum Mechanics without struggling?" The answer is: "Be a person who's naturally good at physics and abstract concepts that really don't make logical sense."
If you simply weren't lucky enough to be born/raised as the kind of person who doesn't struggle in relationships, then it's inevitable that exploring poly relationships will be accompanied by a bit of hurt. In that case, it's probably more productive to come up with strategies for dealing with that hurt, coping with it without limiting other people's lives. Finding strategies for avoiding the hurt all together is basically going to be impossible for you if you're just not wired that way.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker