Setting boundaries probably won't feel great at first, and the other person probably won't like them. And that is exactly why we need to trust the Spirit to give us discernment & strength, and surround ourselves with healthy people who will keep us on our path to wholeness! (Proverbs 13:20, Hebrews 10:25)
So, how do you set them? Boundaries can be reactive: "You've crossed the line, now back off!" But to be healthy & live God's love, we need to move to proactive boundaries: "Here's where the line is, so I'll give you a friendly heads-up when you're within 50 feet of it." (Romans 12:18)
By the way, just as we teach our kiddos boundaries & respect through how to say no & hear no, we need to practice saying & hearing no in our own lives. Our little ones learn from what we tell them, but they also learn from what they see. (Proverbs 22:6)