Few quick thoughts here...
Exercise is one of the best counters for depression. I can explain why if you don't believe that. In most cases it is not a cure for depression, but it helps a bunch.
@Hua Guofang and anyone else who thinks you can't offer advice because you haven't dealt with depression, I would say you still have a lot to offer. What about the opposite side- happiness or contentment? Maybe you have ideas on how to acchieve or maintain that.
On drinking- the obvious best method is to not drink, but how you do that is up to you. To expect someone to turn off one day and never go back sounds great, and some people do that, but the majority of people do stumble here and there along the way. If you put your pants on every morning right leg first, and I tell you starting tomorrow you're going left leg first every time, I can bet your right leg will still find its way there first quite a number of times before you fall into a steady habit of left leg. It can also be a matter of perspective. You said you hung out, had a drink or two, and felt good about that, so feel good about exercising control in that particular situation. After that the rest was a matter of choices- you could have bought or left the whiskey. You could have bought it but then put it on the shelf, or you could open it and have some. You could drink half or the whole thing. You have choices.
I believe I gave credit in a DM for bringing all these things up here but will give it here too, this is the real life shit that a lot of people experience but are afraid to talk about, it's also the type of thing that some people are afraid of or don't know how to respond to, so an old school round of tic-tacs for all.