The speaker looks at their own life and finds it slight. The "business of the self" sounds important, but the poem calls it "thin stuff," and the title, "Bit part," pushes the same idea: we are minor actors in a larger play, spending a little time in some little part.
Then the poem turns uncomfortable. Even in that small role, the speaker admits to dropping "some little violence" on someone they love. It isn't a dramatic act. The word "little" keeps repeating, which makes the harm sound almost harmless, and that may be the point. Small unkindnesses are easy to excuse.
The last line, "as morning bacon," is a surprise. The violence falls the way breakfast does: routine, ordinary, almost affectionate. The mood is wry and quietly guilty. The speaker doesn't make a big confession, but the casual tone makes the admission sting more, as if the habit of hurting people close to us is just part of the daily routine.