Sam is an interesting character. There are three prominent sections where we find out the most about Sam. A good question that emerges is whether or not Sam underwent character development (change in character as a result of growth, understanding, regret, epiphany, etc) as a result of his interactions with Sophy the story progresses.
In the first scenario of interest, Sam interacts with Sophy and offends her because he wants to romance her (in an modest and era-appropriate manner) on a day on which she is in grief and (probably) shock at her mistress's passing, in other words, while she is still exhausted and emotionally drained after the death of the Vicar's wife. Here, Sophy rebukes Sam and enters her parent's home with feelings of disapproval toward Sam's insensitivity to the situation that death calls forth.
Then we find that while Sam and Sophy have become engaged, she is not that keen on marrying him though aware that it will be practical and give her a home of her own. Suddenly, we are told of a quarrel and a permanently broken engagement. We have no clue at all to the cause. We can only extrapolate from the small exposure to his behavior discussed above what Sam may have done to alienate Sophy--for we surely feel the breach was Sam's fault.
Through extrapolating values and related actions, it may be that Sam asserted what Sophy would and would not do after they were married, or perhaps he began to demand more of her physically than she was willing to give before the wedding. What we can surmise is that somehow or other, Sam asserted his will in a way that was wholly unacceptable to Sophy, who has a broader world perspective and higher values of good and right than he does. Perhaps it might be said that Sophy felt Sam was morally beneath her.
The second scenario of interest to a character sketch is when they re-encounter each other. All the initiative for the encounter is on Sam's part; from this we know that his feelings for Sophy have not dimmed over the years, especially since he married no one else. He hears of the Vicar's death. He looks for and takes a job at a grocer's in the neighborhood near Sophy. He learns what street she lives on. He deliberately drives her street to market every day and deliberately looks out for some sign of her everyday. If we accept the idea that we extrapolated above, that Sam was to blame and was somehow lower morally than Sophy, we can see that Sam is not vengeful and that he is very determined and very ingenious in pursuit of his desired end: reunion with Sophy. When they do meet, Sam displays great and completely sincere courtesy, respect, gentleness, thoughtfulness, and kindness. He puts Sophy first in all actions though he does suggest what might be in her best interest and helps to attain her best interest: riding in a buggy, speaking to her son.
The third scenario is his deportment as Sophy's funeral procession passes by. He humbly stands on the side of the road, a participatory observer rather than a participant in her funeral. He is humble, full of deep mourning, and (possibly) full of regret. It is entirely possible, when these three scenarios are examined together, that a character sketch of Sam must include a psychological movement from self-absorption to other-focused sensitivity and to a deep mournful regret that his inability to grasp a wider worldview--seeing beyond his self-interest--led to failed love between him and Sophy and to lifelong mournful misery for both. [This analysis also identifies two protagonists for the story: Sophy and Sam.]
a middle-aged man was standing at the door of the largest fruiterer's shop in Aldbrickham. He was the proprietor, but to-day, instead of his usual business attire, he wore a neat suit of black; and his window was partly shuttered.... The man, whose eyes were wet, held his hat in his hand as the vehicles moved by, ....