I have a half brother

my mom found out my dad had a daughter 9years older then i was, when i was 3 years old, she found out from a phone call. her mom called my dad and my mom answered...i've only seen her like a handful of times and im 18 now shes married with a little girl and i've never met her husband or daughter its like i dont even have a sister, but the point of me writing you was to tell you your not alone, its happened to theirs too, and make the best of it you can't change it and maybe the two of you could get to know each other

So what's wrong with that?