Hi,
You asked how you could tell your fiance and family that you want to quit (in light of the fact that you'd told them this before).
When I quit 'for good', I wanted to shout from the rooftops 'I'm sober!' but people close to me wouldn't and/or didn't believe me. So, I let my decision show in my actions. I made a promise to myself that I was going to change my way of living - and I did. After a bit of time, I was able to talk to a couple of friends and share what had happened - they had already seen the change.
That being said, with a bach. party and wedding coming up, you need to make sure you've got people on board who you can be accountable to and who will support you in your decision. You mentioned both your mom and fiance being affected by your drinking - why not tell them? They may or may not believe that this is really 'it', but if it really is, that will soon become apparent as you begin making different choices in social situations.
Sorry if this doesn't make a lot of sense. I just identified so strongly with your initial post - being inappropriate with guys, taking a whiz in the parking lot (oh my) etc etc and the horrors of the next and subsequent days. The good news? You don't have to go through this again.
I'm glad you're here.
Rowan