old_str = "Hello world-Dear and mary, How are you and How is Work going?"

new_str = old_str.split("and")
new_str2 = old_str.split("and", 1)

print(new_str, new_str2)

#output
#['Hello world-Dear ', ' mary, How are you ', ' How is Work going?']
# ['Hello world-Dear ', ' mary, How are you and How is Work going?']