Well, I am not going to argue this very, very common misconception here, but will rather link you to the respective article on our main site where we explained at length why this particular statement is a wholly modern concept and not at all reflected in Scripture. Jesus would not have had the above mindset when he said what he said in Mat 5:27. See, had he thought so, what he said would translate to it being sinful if a man, married or unmarried, lusts after a woman, married or unmarried. This would have made every attraction between man and woman a sin.... Well, I know that those who use the above argument can wax very romantic about their spouses and go on at length about how they met and fell in love with each other, which, following their own logic, should be a sinful thing they should be ashamed of and repent for.
No no, people. If you approach Scripture from a modern day perspective, you always end up in a pickle. You need to get used to the Hebrew mindset in order to understand.
If you are interested, please read more here: