Max,
Stop being a child, your about to have one! Stop looking to the past for reasons to bail.
Be a man, strap on a pair and deal with the situation you've created.
You say that you'll let down everyone if you walk away from this lady and pay no child support? Well, you'll be a f-in ******* so yeah, I'd say you'd be letting them down? But you'll be letting yourself down more.
Raising a child is not easy and not cheap! If this lady has the strength of character to take this all on, well I have immense respect for her. But you made half of this baby and you need to take responsibility for your actions.
Welcome to the real world.