Especially if this is your first time setting a boundary, there will be an almost magnetic, uncontrollable need to “be nice” and “do the loving thing” and “show kindness” by not following through. In reality, it’s unkind and unloving to enable someone’s toxic, hurtful behavior. Do the nice thing and follow through on your boundary. It may not feel nice, but it’s the best thing for both them and you.