Dear Ali:
Seeing your boyfriend drink alcohol activates the distressing experience you had as your father got drunk and then screamed at your mother and then attempted to have sex with her, the two of them fighting.
That childhood experience is well recorded in your brain and every time you see your boyfriend drinking, this early memory comes alive. You did well to assert yourself regarding him yelling at you when drunk and he hasn’t yelled at you or been otherwise abusive for years.
I think it is fair for you to let him know that it is not okay with you that he attempts to have sex with you when he is tipsy or drunk. On the other hand, I don’t think it is fair of you to demand that he no longer drink alcohol. Some distress you will have to endure as you repeat sensible thoughts in your mind, thoughts like: he is not yelling. If he yells I will protect myself and make sure it does not happen again. I am capable of protecting myself. Etc.
When I find myself distressed over another’s behavior that I can’t and shouldn’t do anything about, I say nothing, do nothing and I feel sad for suffering about it, but I endure it nonetheless. Over time it got better for me, less and less distressing. I believe it will work for you as well, over time.
The wedding you are going to will be your opportunity to practice this enduring. It won’t feel good but the practice is a good thing because it will eventually yield results.
There are other triggers in your day that activate other fears, the principle of dealing with those is the same: assert yourself when it is appropriate, do what you need to do when there is something you should do. Otherwise, endure the distress. You build strength this way, confidence in your abilities, and this by itself reduces anxiety a whole lot.
anita