“End” here means “goal” or “purpose” (like the phrase “the ends don’t justify the means.”). In particular, it means the salvation of his soul–gluttony is a mortal sin when consumption and pleasure become the purpose (the “end”) of life. St. Thomas explains in your link:
“This is the case when he adheres to the pleasure of gluttony as his end, for the sake of which he contemns God, being ready to disobey God’s commandments, in order to obtain those pleasures.”