Yes while it takes two to tango (to have a sexual affair with) and while there was probably already problems with in a marriage to even entice a spouse to go astray....... it still was not the marriage problem that necessarily broke up the marriage, but rather the sexual cheating became the last straw - other wise the marriage may have stood the test of time.

I say this for while my 21 year marriage is far from perfect and we defiantly have problems and issues within our marriage we are still together / still in a marriage together....... but if my husband was to cheat then he would be out the door and the marriage would be over (not if or's or but's about it).

SO YES - another person can break up a marriage.

AND NO - I have never broken up a marriage.