Relationship Advice

So I have a problem. I have been in a committed relationship for 10 years with a great guy who is only a couple years younger then me. We have a great relationship and I have no intention of stepping out or opening the relationship. My problem is that I have a huge dad/son fantasy. I get off to it constantly and my innocent getting off has been leading to searching profiles on Craigslist and gay dating sites and getting off on the fantasy of meeting up with the guy and doing stuff. My fear is that one day I am not going to stop at just fantasizing. This is affecting our sex life and our relationship as a whole bu