Boundaries are by definition, ultimatums.
Boundaries are good things to have because they say to the other person, this is what I will tolerate and this is what I will not. They are the essence of respecting yourself as a person.
Forgiveness is the mechanism that allows a person who has been wronged to move on with their life. You can forgive someone and remove them from your life. It doesn't mean that you have to continue a relationship with them if you believe they will continue to disrespect your boundaries. Forgiveness is not for the wrong doer. It is for the wronged.
Forgiveness is radical acceptance of the pain and any resulting anger. Give yourself permission to feel these things. It means you are alive. Then forgiveness is the conscious decision to let it go. A wise man once said that attachment is the source of all misery. Let go your attachment to the pain. Let go your attachment to the anger. It won't happen overnight. It's a process. It will come back. Each time it does, let it go again. Eventually you will find your peace.
Me: 48 - Married, straight, male
Shiela: My wife.
Suzanne: My FWB
Adam: Shiela's LDR