If he really, "has nothing to do with birth control, never has," then he has relinquished the right to say when he has a kid.
For fun, if I had to speculate why she'd not just go fuck someone else, maybe she want's to have 'his' baby. He is an 'angel' after-all. Sure a young woman can almost always get fucked but she may also be picky about the genetics of the father.
@55 has it right. As much as I am reluctant to use evobio to explain psychology, the fact might well have been that this guy's genes were the best available to the LW at the time. Perhaps she examined her past and (projected) future relationships, determined that this was the best it was going to get, genetically, and made her decision.