People who act like this about people they meet online in a video game make me wretch. Get life, get some perspective. It's a video game. This bizarre behavior usually stems from people who's real life social status is so pathetic, they consider the online associates they meet in video games, as "friends". Sleeping with a RL friend's girlfriend is immoral, what the OP did was not.
Only someone who is clueless about life would find what the OP did was wrong, and probably needs to put the games down for a bit, find a girlfriend/boyfriend, RL friends, a job, have kids, or all of the above.