It is difficult to end a relationship with someone without your children being affected by this decision. This is especially if the person you would like to cut off intimate relations with, is a spouse who is the biological or even surrogate parent of the children. There will certainly be some form of conflict because the children might have pleasant relationships with the parent concerned, and will have difficulty coping with a separation by one parent.
The key so that the children are not hurt is that you have to be honest with them all the time. Be in constant communication with them so that they know how you feel at all times and how the relationship is already affecting you negatively. In all probability, the negativity might be affecting the children as well. Children are very sensitive creatures, and no matter how you try to protect them or shield them from negative events, they will always have a way of finding out the truth.
Being in constant communication with the children will allow them entry into your thoughts and feelings. They may also give their precious opinions with regard to the relationship. The children are part of the equation in the relationship, and thus their opinions matter. If the children see that you are already suffering because of the relationship, then it is very possible that they will understand your decision to end it.
Another important consideration in this equation is that one must provide for the protection of the children if the partner who is being told to go away is bound to become violent. This is what should be always at the back of the head of the person who is to terminate the relationship. The children should not suffer anymore than they already have, and so the parent who will terminate the relationship must be prepared for any eventuality.
By the time the parent is ready to terminate the relationship, the children are already aware of what he or she is about to do. They might not be accepting of the decision, but they are not caught off guard. They know what is about to happen, and they are readying themselves in one way or another. What is important again here is that there is no pressure on the children from the partners to make any immediate decision as to whom to stay with or with who to go to after the relationship is ended. It will be unfair for the children if they are immediately pressured to choose between the partners. Also, if the partnership is a marriage, divorce proceedings would have to be initiated. Again, the children must be prepared by the parent for any eventuality.
Ending a relationship is never easy on any child. The child is bound to suffer and carry some stigma of the botched relationship even after it is over. It is through constant communication and with the guidance of the parents that the child is prepared physically and mentally for such events in his life.