Hi @Sp33dy16 you tried to get sober in the past and always failed. What did you do then? Because whatever it was, it was not enough. If it was simply not drink, you’re in luck, because there are so many other things you can and need to do to aid and make your sobriety permanent. Just putting it down will not suffice. Check out these resources here.
Resources for our recovery
Advice for the Newcomer and Constant Relapser
Also join us on the gym and weightlifting thread if you feel like it! Gym selfies, weightlifting & fitness 
Regarding that stag do, I would cancel. Go to the wedding itself, but leave the stag do out if you’re serious about your recovery. That would be paradoxical for me to take part in that in early recovery.
Wishing you the best!