Please Men and women...give me your ear ???

I have been in a relationship for the past 4 years, I have a really good man(age60) and I truely love him BUT there is a problem. I have this "friend"(not really)......there is this guy(age30) that I met about a year ago who I thought was and is the iest thing on earth, he kept trying to get with me and I kept pushing him away, however, recently we have been corresponding quite a bit and I must say, I really like him and I know that he feels the same, I refuse to hurt my man because he does not deserve it but every time I run into this other person I just can't stop fantacising about him and wanting to break him off a little something(but I haven't and I won't), this man is sooooo y and I find it hard to not flirt with him when we speak, he knows how I feel so he won't stop trying to break me down and he is just too y, he is fit and built and tall and handsome and clean shaven and just plain Y. How do I stop thinking about this man in a ual way??I am 24 years old.Help!