He's self-medicating with alcohol to relieve pain. He probably suffers from low self-esteem and loneliness, and may feel unworthy of love. So for him, the benefits of getting drunk outweigh the costs.

Physiologically, he probably has a depleted endorphin level and alcohol provides temporary relief. Love stimulates the production of endorphins, and lack of love may be his problem. Eating can also stimulate the production of endorphins, which probably explains his weight problem.

So the real question is: how do you help your brother overcome his pain?