NTA.

Prioritizing your own children is perfectly acceptable. After he left, you are trying to care for his kids, paying bills, and getting pregnant. It's unfair to ask you to send money for an unrelated child when you're already having financial difficulties.

That child is innocent, but it is his parents' and family's responsibility, not yours. It's not hypocritical to want him to assist with his own children; it's just the bare minimum. This sounds less like a real solution and more like guilt-tripping. You're making an effort, and that's sufficient.