There isn't a clear antagonist in Middlemarch the way there is in many other novels. The source of most of the misunderstandings and dissatisfaction in Middlemarch is the inability of characters to reconcile their ambitions and desires with the everyday realities presented by conventional Victorian society. For example, Lydgate can't follow through on his dream of making a great discovery in the medical field because he gets up to his eyeballs in debt and the stodgy medical community in Middlemarch isn't interested in changing the way they do things. Dorothea wants to reform the world and do great good, but she's thwarted by the fact that she's a woman and because her friends and relations keep shooting down her ideas. Will Ladislaw is discontented for most of the novel because conventional society doesn't trust the fact that he's not 100% English, and because conventional social norms won't allow a poorer man to marry a richer woman without accusing him of marrying for money.