Alcohol affects judgment first, so if he's buzzed or drunk enough, he probably bought it with an ulterior motive. That doesn't necessarily mean it has to be sexual in nature, he could just want basic platonic company for a few minutes.
Most people in their 20s, as they gradually approach their 30s, start drinking at home instead because it's cheaper to do so. The average cost of 1 drink in America is about 1/3rd - 1/2 the cost of a fifth of liquor here at a liquor store. You *can* find places that go cheaper, but that's the average price range and scale.