If you're Catholic, talk to your priest about annulment. If you're Jewish, talk to your Rabbi about a Get. Because a legal separation is just as complicated as a divorce, and you won't be moving on with your life if you remain married to this person. (Also, what are the odds he's not going to turn around and divorce you... I've seen that happen countless times, with the wife suffering through an abysmal marriage because she "doesn't believe in divorce" only to be divorce by her husband the second she suggests separation.)