OP. People (especially men), say all sorts of things at the start of relationships. They want to be viewed in a nice light, want to be seen as a good guy, good man etc etc. This is to make you feel all warm and fuzzy, lock you down and get what they want (sex and/or the benefits of a relationship).
Of course he wasn't just going to say out loud to you, when talking about a hypothetical baby or hypothetical unplanned pregnancy- "well actually if this happened I wouldn't be supportive, I'd want you to have an abortion and I'd be planning to f*ck off and leave you alone".
Often people just say what they think you want to hear, or what makes them sound like a nice, reasonable person.
By his reaction, he was clearly hoping this didn't happen.
Did he know you were off the pill OP?
And I say this as someone who's been in a sort of similar situation, although we'd been together a bit longer than 6 months!
He told me "oh I would be so nice to have children with you one day" etc.
But when it actually happened, he was not on board at all.
He wanted to "stay" together. But really this was just so he could get in my ear and tell me "I want a baby with you but just not right now, the timing isn't right" I.e try and convince me to have an abortion.
He's an EOW Dad now (pretty reluctantly I might add!) and does just enough not to be seen as the "bad guy" or a "deadbeat".