Although he didn't admit it, he still had that childish fantasy about their happy ending, especially since he considered Vanessa and Mark the perfect couple. This showed that although she has been independent and strong from the beginning, she is still a teenager at the end of the day and some real life situations that most adults go through, such as divorce, are complicated for her to understand and deal with. In the end, he kept his promise and gave his baby to Vanessa anyway even though she would remain single