Ok.
I know it must feel crap, and you are thinking why did he want those children, and not mine. Maybe this will take the emotion out of it.
Could be a lot of reasons. Perhaps his first DC were planned so very much wanted. Perhaps he was in love with/married to their mother and wanted to be a family unit with her. These things are not the same with your pregnancy.
He's probably fuming at himself for not taking better precautions on one night, because that one night is going to transpire into a huge amount of money he has to pay for the next 18yrs. His anger is then seen by you.
If he's 45, I don't know how old his DC are, but I'll hazard a guess at 15 and 13, if he had them at your age. He did the baby stuff so long ago. A baby at 30 is not the same as a baby at 45. He was looking at being "child free" in maybe 5 years or less, and you've just added 18yrs to that, and there's nothing he can do about it.
I know certainly, from having DC1 at 26, then DTwins at 37, that I feel ten times more tired. I look at DS who's now 15, and sometimes think FFS I'd be free and have my life back in 3yrs if I didn't have DTwins, I'd only be 43. Now though, I'll be 55 when DTwins hit 18. 26 to 55 is a long bloody time to raise children. The age gap is my only regret about my DC. Your baby's father will be 63 when it turns 18. That's a hell of an age, 7yrs off 70 when your child leaves school.
Can you see why this isn't personal, against you and your baby, but probably why he's made the choice he has? Maybe it's easier to process facts without the emotion. It's not that he doesn't want your child, he doesn't want any child. And he's furious with himself he let this happen, furious he has no choice in the matter, and you are seeing this from him.
I get that this might not be the ideal situation to announce to your family, and they may have questions, but you don't have to be frightened of this. "Why have you decided to have a child without a father?"..."Because I wanted this child, and I know I'm going to do brilliantly on my own, and I hope I have your support.".
You don't have to answer to anyone x