Paul Tibbets NEVER regretted the dropping of the bomb. He requested an unmarked grave because he didn’t want to draw unwanted attention when he died.
Tibbetts was cremated and his ashes interred over the English channel iirc. He spent a lot of time flying B-17s on combat missions to Europe.
Anyone who took sheer emotion out of the equation would see that it was necessary. Millions would have died in an invasion of the Mainlands.