Let's be honest..it happens: You meet who you think is Mr. Right and then you find out he happens to be in an unhappy marriage. Things aren't working out too well with his wife but he can't leave her because of the kids. But give him some time and he will eventually leave her and in the meantime you are falling head over heels for him as he woos you and makes you feel great whenever you are together. If he treats you like this then he will eventually leave the Mrs.
WRONG! If he was a good, honest man he wouldn't be cheating on his wife and if he was then he would either get a divorce or end things with you.
I heard a story from a friend this weekend about a woman who was having an affair with a married man for 15 YEARS! Eventually he divorced his wife and instead of marrying his mistress he found a young 25 year old and married her instead!!
Don't wait around for him to leave. Believe that someone else is out there for you who isn't taken and that you deserve 100%.