hi czbones, sounds like you have mixed emotions going on. i found my son after losing him for 30+ years. from experience i don't think your girlfriend would be happier if you left her. why? cuz just because she's found her mom doesn't mean she wants to shut out the other ones in her life. my son has an adoptive family and there's no way i'd have wanted him to shut out people who loved him too. when he and i found each other he had a girlfriend. she actually came down with him to sc from manhatten, ny to visit me too.
so it goes both ways, meaning the more loving people in our lives the richer our life is. i'm sure your gf feels the same way. losing you would be like finding someone you lost-her mom- to lose someone special in your life...you!, IMHO.
i hope this helps you sort out your conflictIing thoughts.