It sounds like you had a pretty rough day.
You'll get to use the dress - and it will be worth more because the wedding will be to someone who is capable of returning your love and valuing you and your relationship high in their heart. The only way it would have been a wasted dress is if you had gone through with it, marrying yourself to the quagmire of addiction. But it will be hard, and I know it must hurt.
I haven't had to do it, but I know some people on here have and I've read about requesting a police presence for this type of scenario. I think it's not really that dramatic, they just send an officer over. They don't use sirens or flashing lights, any drama comes from the addict. I would do it. If I've learned anything from my sister's drug use and jail record it is that addicts DO NOT like to hang around when cops are on the scene.
I hope today goes better; you tried, and all we can do is keep trying. I find myself falling back into old habits sometimes, it's just part of our version of recovery. But you recognize what's happening - and that in itself is a major step in the right direction.