By providing mealworms as a supplement you did the very best thing you could do. It is normal and quite common for a single adult male or female to raise chicks. As long as they hatch in temperate weather they usually survive just fine. Trouble comes when the female goes missing before hatching or before a day or so after that. Trouble also comes when the female goes missing in cool weather and can’t brood the hatchlings to keep them warm. When at all possible, a single adult will continue to feed the chicks because that is the biological imperative at work.
Congratulations on your and his success!