At the same time dont let someone else's opinion bother you this way
THIS ^
Co-incidentally, only yesterday I was with a group of friends, and over coffee the conversation wandered onto - "If you had your life again, what would you do differently?"
EVERY SINGLE ONE OF US agreed that we would take no notice of other people's opinions of us. If we were happy with how we looked, dressed etc, we wouldn't allow anyone to bully or embarrass us into looking/ dressing differently.
And this especially applied to the opinions of people we neither liked nor respected - we all had a tale to tell about how we'd been made to feel like crap by someone's nasty comment - often at school - by a bully, surprisingly often at work - by a bully, occasionally on a night out - by a bully we didn't even know, but whose spiteful comments made us feel humiliated and destroyed our confidence, often for months.
Your BF's father is a bully. He's bullying his son, and his son is bullying you. As PPs have said, this is a way to control and manipulate you - it will get worse, and one day you will turn round and see that you are married to his father, because the two will be identical in all the ways that matter.
I'd be willing to bet that your BFs mother and sister lead miserable lives at the beck and call of this horrible man - and that will be you, too, if you continue with this relationship.
do something that makes you feel good about yourself, with someone whose company you enjoy if you can - go out for lunch with a friend, have a makeover if you still feel that you have "flaws" (we all do, my love - it's part of being human - you're only conscious of your own minor imperfections because these bullying men have forced you to concentrate on them).
I have met stunningly beautiful girls with nothing behind the mask and who are as boring as fuck - and I've met very plain ones who were incredibly sexy because their personality shone through.
The odds are that you lie somewhere in the middle regarding your appearance - and I'll bet that when you aren't worrying about your appearance , you are an absolute joy to be with.
Get rid of him - he isn't worth (to put it crudely) the team off your piss!
He will most probably come snivelling back to you - ignore him. He is looking for someone he can manipulate and control. Perhaps his first wife divorced him because of this, rather than his infertility (you've only got his word for that - I assume he hasn't shown you his sperm count report - it could be a play for sympathy).
Keep busy, meet other people and be happy - you won't be with him.