Oh my gosh someone help!

I've been dating my boyfriend for about 3 years.

My mom died when I was little so my dad raised me (I'm 20.) My boyfriends parents are divorced. He lives with his Dad (he's 22)

So we've talked about the next step (getting married)

Couple weeks ago found out I was expecting. We wanted to wait to tell my dad until we were sure and had an ultrasound picture.

So dad said we'd be having company (his girlfriend of a couple months who I've met maybe twice so I was like okay that's cool. My boyfriend has never met her)

So we decided to meet them at a restaurant. My boyfriend and I go to sit down and he goes white like a ghost. Here it is ladies:

MY DAD IS DATING MY BOYFRIENDS MOM AND THEY HAD NO IDEA

And here I am pregnant with boyfriend who is my dad's girlfriends son. Holy fuck

WHAT DO I DO?!?!?