If you believe in your marriage, that's great. It's not that temptations or invading and uninvited thoughts that come that is so wrong it's if you pursue them and even just entertain them in your thoughts. That is playing with fire but the fact that it seems that you're kind of obsessed somehow with this guy, I agree with the others that something may be missing from your relationship with your husband. If you do love each other and from waht you've said I have no reason to think otherwise, I think that you should communicate with your husband about what's missing when you figure it out. (not about the other man, of course don't do that!) I am sure that you can work something out that will help you two to come together as a couple and enjoy things more. Let him know how and what you're not happy about, but remember to let him know also that you're not completely unhappy but that there are some things you'd like to change in your relationship

Counseling if it's an option for you would possibly be a good idea before there is a rift that forms between you, because at that point counseling, in my opinion, becomes tougher to work through.