James, I felt exactly the same way. I didn't want to "let my boyfriend down"...
With this disease you need to be selfish and think what's best for you. My bf can have two and stop. After I get two I can't stop.
Now when I go out with him I keep thinking: when I get another dui or something even worse happens, he won't be in jail with me. I can't blame him on anything. If I drink I will be my responsibility.
And that thought keeps me sober. It's still not easy to be the "boring" one but when time goes by he and my other friends get used to me being sober and I can be the one waking up early making them breakfast when they're all having a hangover...