My sister couldn't have children. She told me once, I'm not jealous or anything but I see people with two or three and I wish I could have just one. I told her I would share mine with her and she could borrow them whenever she wanted to. She laughed as I intended her to. She passed away several years ago but she could not have been a better aunt to her special nephews. I sure miss her sometimes.
Yeah, I know the feeling. :-)
You can't be bitter about it. It will just eat you up inside.