I almost broke up a couple, but not through my own actions. I told my friend I liked a guy, my friend told the guy, the guy liked me back, and he almost broke up with his gf. But in the end, we didn't go out and he broke up with his gf anyways because they were having problems.
i never cheated.. but i've been cheated on before.. and i think i am the cause of some friends' breakups.. ohh well