Why couldn't Larry and Gwen have a happy ending?

They haven't know each other long enough to develop an attraction but I really hoped they'd have more time and that Larry and Gwen ran off together. Say he couldn't kill her cause wolves mate for life or if they had sex and Gwen was expecting his baby then he knew he couldn't cause he hears his baby in her. While he sees others as food, he sees only Gwen clearly as his mate.