I think you can't control this, can you? You can be honest about your feelings and explain yourself to her, and you can try to find new lovers for her, but if she wants to see one regularly, can't stop her. I guess it's not the question whether or not it will happen, the question is WHEN will it happen, and will your relationship survive it? I would tell my gf the truth, but would not hold her back if she wanted to leave me.