Does he need to be in a relationship with her?

One of my very best guy friends was seeing a woman casually for a month or so. They had a mishap, and there's a chance that she could now be pregnant. He is fully willing to take on the responsibility of being there through everything, but he doesn't want to commit to a relationship with her just because she might be pregnant. She, on the other hand, has become super clingy and controlling. She has made it clear that she wants a relationship, and she got very defensive and angry when he tried to discuss it with her. What should he do?