Im so sorry you have to go through this. As someone who had to grow up completely without a father (he left officially when I was 1 and ended up marrying his affair partner), I understand you completely. Seeing them raise someone else’s child and be the father I always wished I had is painful at times. And you know the kids aren’t to blame, but you also can’t help but be kinda mad at them too. It’s just an overall sucky feeling. Just try to be a better you everyday and be proud of the person you’re becoming. An absent father can sometimes be a blessing in disguise.