Now, 40, I was 16 when a work associate of my father's gave birth to what is my half sister. Apparently my father and the woman were the only two who knew who the real father was - until I was looking at pictures about six years ago and noticed that, not only did my father have tons of pictures of this kid, but, yes, she did look exactly like him. I confronted him about it and he finally fessed up to it after some initial denial.
No one would have thought to question it before, because the woman was happily married and still is. We also would go out to eat with their family. She was an only child, which leads me to believe/think/theorize that the woman tried to have kids with her husband, couldn't, so picked someone she liked to father her child. I'm hoping that theory is correct. And apparently the girl (my half sister) doesn't know. The only one who knows the whole story about who knows, how it happend, why, etc., is her mother.
I recently saw my half-sister for the first time in about 15 years - since I took my father to her wedding. My own wife has been saying I should speak to my half-sister's mother to find out what's going on. And my wife suggested that if my half-sister didn't know, that she didn't need to know who her real father is.
I have my own reasons for wanting a relationship with my half-sister - a) she's my sister, b) if she has chidren, they will be my neices/nephews, which I don't have, c) my children will have cousins, etc.
I also have reasons not to have a relationship with her: a) she's 24 already, I'm 40 - a lot of time has passed, b) it might blow her mind or ruin her mental state, even if she is a level-headed person, c) she has a loving family she grew up with as her family, and her father probably doesn't know he's not her real father; so it could tear her family apart, since there would be recriminations, dishonesty to deal with, d) she might resent the news or offers of other family relations, e) she might sue my father for back-child support/inheritance, etc., and f) if she doesn't know, it will be a complete shock to her and maybe it's better she doesn't know.
It's a touchy situation all around, but in the end, she is my sister. My full brother and full sister - both older than me, have mixed feelings; my full sister wants no relationship with her half-sister, while my full brother is wait and see.
Any advice? Is there a logical step here to deal with this? Has anyone dealt with such an issue before?