Complex sentence: About 1933 Kirby left Henderson to play with Chick Webb (twice), before returning to Henderson, and thence joining Lucky Millinder; he briefly led a quartet in 1935, but was usually employed as bassist in others' groups.
Split into simpler sentences: About 1933 Kirby left Henderson and played with Chick Webb (twice), back with Henderson, and with Lucky Millinder. He briefly led a quartet in 1935 but generally kept busy as bassist in others' groups.