Given the major traits that link the cast of The Return of the Native (dissatisfaction, poor decision-making skills, faulty judgment, depression, pride), it's no wonder that guilt and blame come into play in spades. In particular, these troublesome two define many of the relationships we see here. The bulk of Eustacia and Clym's marriage is dominated by feelings of guilt and blame, especially on Eustacia's part. The notable exception to this guilt-fest is Diggory Venn, who's upset about his situation with Thomasin, but doesn't feel guilty about it. Nor does he really seem to blame Thomasin for her decision not to marry him initially. Diggory may have the right idea here – in the end, guilt and blame usually amount to nothing. It certainly didn't get Eustacia, Clym, or Mrs. Yeobright (the ones doling out the most guilt and blame here) very far in life.
Eustacia handles her own feelings of guilt by blaming her problems on fate or destiny.
Diggory is one of the few characters who doesn't suffer from feelings of guilt or blame; he is sad over his situation with Thomasin, but he doesn't blame her for it, and he doesn't feel guilty about it.