I would tell your husband too. If he finds out some other way, he's going to be more hurt than if you tell him yourself. You could just be honest and say this was an old friend who doen't get the hint.

Delete this guy from Myspace. As long as he has a way to contact you, he's not going to stop. Granted he can still call, but internet is much more secret way of contact, so delete him. Tell him again that you're working on your marraige and he needs to leave you alone. And I would really tell your husband.....so that just in case this guy does try and blow your cover, your husband is already aware. Nothing happened aside from talking, right?