In your first post, you posted "what do you think?" asking for opinions. People gave their honest opinions. You also stated that as long as you've been doing this, you didn't see anything wrong with what you're doing.

Then you later said it's a problem and admit it's an addiction. Now that you realize it's a problem, what do you do about it? You see a professional and talk to them about it. You probably need a sex therapist, or someone who specializes in sex addictions.

People tell you it's only fair to tell your fiance because she has a right to know what she is getting into, just like with any other addiction. If you fear you're going to keep doing it and you do not have an open relationship where sex with others is allowed and OK, why not delay getting married or not marry at all? Your fiance is going to have a rough time with this in the future, if it continues the way it has been. You do need to think of her well-being in this matter too. I hope this is helpful.