“I feel thin, sort of stretched, like butter scraped over too much bread.” - Bilbo Baggins

Tolkien wanted to show how the ring had different effects on the various people who carried it, and also how the ultimate effect was negative. Bilbo wanted to live a long, comfortable life, and that’s what he did, but here he recognizes that it’s too much.

Gandalf later says that he could wield the ring for good, but eventually it would turn him in to another Sauron. So the ring has to be destroyed.