The soviets were patronising. Mao resented Stalin's operatives telling him what to do all the time pre 49. Post 49, nothing much Russia did was in China's longterm interest. China and India were in border dispute which still rancours yet the soviets wanted some degree of amity with India, leading the non aligned nations in the UN there was much for them to profit from not supporting China across that boundary dispute. The Korean war probably started overt resentments which had things like inner/outer Mongolia to stew over since day 1. When Russia blew hot, China was cold, and vice versa. When Russia went with peaceful coexistence China was still militant. In the end, they were "much too much in love to get along"