Love is blind

A guy went up to his father saying:

"Daddy, I fell in love and want to date this awesome girl!"

Father: That's great son. Who is it?

Son: It's Sandra, the neighbour's daughter.

Father: Ohhhh I wish you hadn't said that. I have to tell you something son, but you must promise not to tell your mother.. Sandra is actually your sister.

The boy is naturally bummed out, but life goes on, and indeed, a couple of months later ...

Son: Daddy, I fell in love again and she is even hotter!

Father: That's great son. Who is it?

Son: It's Angela, The other neighbour's daughter.

Father: Ohhhh I wish you hadn't said that. Angela is also your sister.

This went on couple of times and the son was so mad, he went straight to his mother crying.

Son: Mum I am so mad at dad! I fell in love with six girls but I can't date any of them because dad is their father!

The mother hugs him affectionately and says:

"My love, you can date whomever you want. He isn't your father".