I see a bunch of red flags here the biggest one being that you feel you can't tell him the truth because he is jealous.
The pre party is about drinking right? That's why transportation is being provided right?maybe that is also triggering something in you...
Maybe you do need some more space?are ya'll living together? Maybe things are moving too fast?
I think if the guy is as good as you say he deserves your honesty the longer you wait about this the harder it will be when he finds out. Unless you feel that you don't really know if you want to tell him about your real past because you do not trust him then you owe it to him and you to end it..