Advice please!!

So I'm 23 and 11 weeks pregnant with my S/O of 3 years who's 34! He's has 2 children from a previous relationship. He recently found out that his ex partner is letting their 16 year old daughter have random boys stay round and surprise surprise she's now pregnant!! He's kicking off, but now I think it's weird that he's going to be a dad over again and a grandad at the same time! I don't want my child having nieces or nephews at the same age of it. I think it's really weird! Am I being wrong? I'm now re-thinking my whole relationship and cuting ties and doing this mum thing on my own. His daughter has said there is FIVE potential dads! And that she only got pregnant because she didn't want us to have a kid!! I'm totally heartbroken but also very angry! Advice please x