Why did the Socialists separate from Congress to form a separate Socialist Party in 1948?

Congress amended its constitution to prevent its members from having a dual party membership.

The Socialist Party originated during the mass movement stage of the Indian National Congress in the pre-independence era.
In 1934, a group of young leaders formed the Congress Socialist Party (CSP) within the Congress, seeking a more radical and egalitarian approach.
In 1948, Congress amended its constitution, not allowing its members to have dual membership, forcing the Socialists to form a separate Socialist Party.
The Socialists differentiated themselves from both the Congress and the Communists by advocating democratic socialism.
The Socialists faced a dilemma when Congress declared its goal as a socialist pattern of society in 1955 (Avadi Resolution), making it difficult to present themselves as a distinct alternative.
Some Socialists, led by Rammanohar Lohia, distanced themselves from and criticized the Congress, while others, like Asoka Mehta, advocated limited cooperation with the Congress.
The Socialist Party experienced splits and reunions, leading to the formation of various socialist parties such as the Kisan Mazdoor Praja Party, Praja Socialist Party, and Samyukta Socialist Party.
Notable leaders of the socialist parties included Jayaprakash Narayan, Achyut Patwardhan, Asoka Mehta, Acharya Narendra Dev, Rammanohar Lohia, and S.M. Joshi.
Several contemporary Indian parties, including the Samajwadi Party, Rashtriya Janata Dal, Janata Dal (United), and Janata Dal (Secular), trace their origins back to the Socialist Party.