DEAR ABBY: My daughter-in-law, “Louise,” died of cancer five years ago. She was 45; my son, “Pete,” was 48. They’d been married for 15 years and had no children.  Three years ago, Pete met “Shelly” through a mutual friend, and they were immediately attracted to each other. Within a year, they were living together and seem very happy. Shelly has two grown children and three grandchildren. Her mother is also in the picture. I have met her a few times, and she was very pleasant.  What bothers me