UsefulAlt
As someone who found out the hard way - 100% fully agreed. I loved my father (mother too) very much, and they, me.
And now that I know the truth and they have both passed, we can never talk about it, and there is a thorn of resentment that, frankly, I do not know if I will ever be able to fully remove.
(I found this out through 23AndMe, when I was contacted by a half-sister I didn't know I had, who was looking for information about her genetic father. Turns out her family lied to her about her origins too.)
To find out that I was half-adopted myself didn't bother me at all in one sense- I loved my Dad, and that didn't change. But I now have real anger towards the fact that neither of my parents told any of us the truth while they were alive, and maybe my relationship with my sisters would have been different if we were all at least a little in the same boat. My parents were loving people, but were just from a generation where things like this just weren't talked about. Like an earlier poster said, it's all just... Vexing.
The one thing I am certain of is that finding out your Dad wasn't your biological father while dealing with spiteful siblings who are trying to destroy you for the vulgar, prosaic money reasons that often erupt in families as the estate was divided was a supremely shitty way to find out. Tell the truth early and often, and hide nothing.