I think you got that exactly right. Jack is seen as "not man enough" by people around him several times during the movie. And my heart bleeds for him every time.
Take a look at the scene with the rodeo cowboy earlier in the movie: Another scene of rejection, of subtle contempt. No wonder he thought he had to marry. The tragedy is that it doesn't really help either. In a society where being a man is equated with being rough, unfeeling and even kind of dumb (witness the father in law), Jack just doesn't fit in.
monicita