The Enemy (1916)

Famous architect Harrison Stuart is taken over with alcoholism and begins living in flop houses, he is saved by Billy Lane, a young architect who has always admired the older man. Lane reunites Harrison with his family and falls in love with Harrison's daughter. After announcing his engagement to her, however, Lane himself becomes an alcoholic when another woman, jealous of his fiancée, spikes his punch and tricks him into heavy drinking. Then Harrison gives in to his old habit but before submitting completely, he kills himself. The suicide brings Lane to his senses; he swears off drinking and returns to Harrison's daughter.