I would bet you could tell the age of the member based on the advice given. The "school of hard knocks" group has a lot of experience and good reasons for what they are saying.
Telling fiance is your way of trying to avoid what is the real problem here....you haven't grown up emtionally yet. If you love her why is it that you are so willing to hurt her? It is your problem and now you want to make it her's too?
"Oh baby I love you and I bonked my ex last week. How are our wedding plans going?"
Listen to what your actions have told you. In a round about way you set it up so your fiance will do what you haven't had the ***** to do, call off the wedding. Your ex counted on you playing the role of "chump" why is it that she knows you better than you do?
I seem to be harsh you? You can bet this is how these women are going to treat you in the future. What kind of relationship starts out with cheating? Have some self respect and don't put these women in the position where they can treat you poorly for ever.
Tell the fiance you need to hold off on the wedding, you need to grow up and then marry her. If she's still there then it's all good. If she has moved on then she wasn't really "the one".
We have friends who were married when they were 18, they had a great marrage. I think the chance of this is slim, add to it you can't trust yourself, things don't look very good. Be a man, don't do squat about the ex and her "5 day's late game" wait for her to say something. Meet it with a firm response that there must be testing done before you will coment. Tell your fiance you are not able to marry her now. Pay her family for any expenses they had because of the wedding plans. Get your head together.