The absolute last thing anyone needs is for this total piece of shit to marry the 15-year-old girl he knocked up. He hasn't learned anything or grown up a day since this nightmare started. He's still to the core a coward who cares about nothing but his own selfish desires and comfort.
What he needs to do, first of all, is to take full responsibility and try to help his wife and child. Not apologize unless that's clearly what they want. Not try to "fix things" unless that's clearly what they want. He needs to stop running away, engage with his family, find out what they want/need from him, and DO IT. Even if all they want is to never see or hear from him again.
At the same time, he needs to support the teenage mother of his child-to-be without saying a word about what he wants. If she wants an abortion, he needs to pay for it without complaint. If she wants to have and raise the kid, he needs to pay for that, too. In either case, he needs to get her the assistance she needs to legally separate from her mother.
And no matter what, other than providing financial support, he needs to immediately and forever get the fuck out of her life.