DEAR ABBY: I’m a millennial. I am successful in my career and lucky to have a loving husband and two amazing children. I am, however, trying to remind myself to be “better and not bitter” in another huge area of my life. The world is changing so quickly, especially in the field of in vitro fertilization. I know I have much to be thankful for, but I’m finding it a hard pill to swallow that many of our older parents are choosing to have another set of kids in their later years. My father, who is in his mid-60s, has just had twins with his third wife. His children are younger than mine. I feel en…