From a guys perspective, you have to decide if you are happy with your husband or not? If the marriage great, or are you willing to cheat on him? If you are willing to cheat on him, its better to tell him you think you want a divorce and why. He may tell you that he is fine with you screwing other guys and cant imagine life without you. He may tell you that you are all sorts of nasty things.
The simple fact is, once you are in a relationship where you both are choosing to be only with each other, its not fair to make the decision to be with someone else. You can determine that you want it, but you have to decide how badly you want it. Is it worth losing your marriage over? Do you love him enough to tell him you have a fantasy that involves sex with someone other than him? Maybe he will tell you he is fine with it. Maybe he will expect the same level of permission from you in return.
Some people just live in fear. They are afraid to be themselves out of concern that they will be judged harshly. So, just be honest with him and let things go how they go. Because, nothing is worse than getting cheated on, and you would hate him if he did another woman behind your back.
Once that is settled, then you know if you are still a married woman or not. You know if your marriage is most important or not. You have been talking with this guy for a long time, but have you been doing it behind your husband's back? I'm not judging you, I'm just trying trying to help you determine what you want. If its BBC, that's fine. If you want it even if it means you get divorced, that's not a problem.
Just don't leave him in the dark. You care about him, so treat him with respect and be prepared for whatever comes from your desires. It's fair to you, and to him.