Breaking up someone else's relationship is not an acceptable behavior. It may not only ruin their relationship but your reputation if found doing things to cause break-up of two persons. Also, there is no guarantee that you will have a good relationship with someone if you do that. The best way to achieve a good relationship in the future is to move on and nurture yourself instead of looking for ways to break someone else's relationship.
Breaking up someone else's relationship may not be a difficult task, but it is just not a good idea. There is not really any gain in it after they find out it was a created breakup and they know it was you. Move on and enjoy your life and spend your energy on something worthwhile.