Jas, i think i know what you are going through. same situation. For me.. i moved out. in fact i moved to another country.
finally after 6 months, he get the point.. and now is in the messy process of thinking how to divorce.
sometimes, its not some big story, sometimes it is. but there is no use using adultery to force divorce on him.
the only thing you can do now - if he refuse to just say good bye - 4 years seperation. No other way. the MOST important thing now.. is to let your parents know, and get them to support you. they liking him alot is no basis for you to be intwined in something you dont want. I hope you are sure and definite about the decision. as long as your parents agree with you, he will have no choice but to leave..