Why does Tertius Lydgate’s marriage to Rosamond Vincy fail in Middlemarch?

In George Eliot’s Middlemarch, the marriage between Tertius Lydgate and Rosamond Vincy fails due to a fundamental mismatch in expectations and character.1

Lydgate, a progressive doctor, initially pursues Rosamond because he perceives her as "polished, refined, and docile"—qualities he desires in a partner. Conversely, Rosamond enters the marriage under the mistaken belief that Lydgate possesses significant wealth and will elevate her social standing.1

The relationship deteriorates as these illusions vanish:
* Lack of Intellectual Connection: Lydgate discovers that Rosamond is shallow and entirely uninterested in his medical research and professional passions.1
* Financial Strain: Rosamond’s insistence on an expensive lifestyle, coupled with Lydgate’s actual lack of funds, pushes the couple to the brink of financial ruin.1
* External Pressures: Their marriage is further strained by Lydgate’s professional struggles and his entanglement in the scandal surrounding the banker Nicholas Bulstrode, which eventually forces the couple to leave Middlemarch.1

Ultimately, the union is characterized by mutual disappointment, leading Lydgate to view his own life as a failure.1