Hurts. When someone you're dating decides they just don't like you, or think that things won't work out, after a time of getting to know you, this is painful, but it’s just another part of dating. You move on. Happens all the time.
When someone who is supposed to be your birth father denies your existence even while you are in the womb, then again as an adult, never having met you or known you, this is a rejection of a stranger. It is non-specific. It doesn’t have anything to do with who you are, or your worthiness. This kind of rejection is even less individualized than that of a rejection from a literary magazine that decides your work won't fit with the current issue, or of a company that decides you aren’t the right candidate for the job. This kind of rejection is not rejection, really. It isn’t supposed to hurt.
But yet it does.