One way in which Hugo successfully portrays Marius as divided between his love for Cosette and his friends' revolutionary ideals is by portraying Marius as first seeing Cosette well before he begins getting very involved in his friends' way of thinking. He first sees Cosette in the Luxembourg Gardens around the same time he begins joining his friends in their meetings in the back of the cafe. At first he is indifferent to Cosette, but then falls deeply in love. Similarly, at first he is astonished by his friends' beliefs but then grows to accept them as his own. Interestingly, by the time he has fallen deeply in love with Cosette, he has also completely changed his political beliefs, showing us that both Cosette and his friends represent, or symbolize, an awakening within Marius. However, as his relationship with Cosette progresses, he begins caring less and less about what his friends are doing in the back of the cafe. He begins to spend more time with her and less time with his friends planning a revolution, showing us that Marius becomes torn between his love for Cosette and his political ideals.
Later, when Valjean moves Cosette away from the Rue Plumet, Marius feels that he has lost everything of value in his life and wants to die. This is why, when Eponine tries to distract Marius from Cosette, telling him when he finds her house empty, "Your friends are waiting for you at the barricade of the Rue de la Chanvrerie," he immediately heads for the barricade (Vol. 4, Bk. 9, Ch. 2). He no longer really cares about upholding political ideals. He only cares about his love for Cosette and wants to die now that she has been taken from him, as we see in the lines:
The voice which has summoned Marius through the twilight to the barricade of the Rue de la Chanvrerie, had produced on him the effect of the voice of destiny. He wished to die; the opportunity presented itself; he knocked at the door of the tomb. (Vol. 4, Bk. 13, Ch. 1)
His desire to die shows us that not only was he torn between his love for Cosette and political ideals, his love for Cosette won in the end, becoming the most important thing to him, more important than the revolution.