Vibhishana seeks refuge of Sri Rama

Hearing those harsh words from Ravana, Vibhishana wielding a mace in his hand, soared high into the sky, along with four other demons.  He cautioned Ravana to be alert and be happy, and together with four of his companions reached Sri Rama's place. Halting in the sky itself, Vibhishana introduces himself and his companions, narrates what transpired in Lanka and asks Sri Rama to give a refuge to him. 

Sugriva tells Sri Rama that he cannot trust Vibhishana for he may be a spy of Ravana and suggested to kill him along with his ministers. Then Sri Rama asked for opinion of the leaders in his group. 

Angada, Sharabha, Jambavan and Mainda expressed their apprehensions to accept Vibhishana.  However, Sri Hanuma advised to accept Vibhishana giving logical explanations.

Hearing Sri Hanuma's words, Sri Rama says that he cannot desert Vibhishana, who is seeking a refuge in him. When the assurance of protection having been given by Sri Rama, Vibhishana descended joyously from the sky to the ground along with his faithful companions and fell prostrate before Sri Rama.

Sri Rama asked Vibhishana to explain in detail the strengths and weaknesses of demons. Vibhishana explains him all the details he knows and promised to extend his help in killing the demons and in attacking the city of Lanka according to his strength.

Sri Rama on his part, duly delighted, embraced Vibhishana and ordered Lakshmana to anoint Vibhishana as the King of demons with water of the ocean. Lakshmana consecrated Vibhishana as a king, as per the royal instructions, amidst the leaders of Vanara-s.

Afterwards, Vibhishana suggested that Sri Rama to seek ocean as his refuge. As the immeasurable great ocean was expanded by the sons of Sagara,  Sri Rama’s ancestor, the great ocean would be inclined to do a favour to Sri Rama. Sri Rama agreed to the proposal.

Was Vibhishana desiring to become the King of Lanka and thus helped Sri Rama? 

As the elimination of Ravana is looming around, he might have decided to join Sri Rama and to accelerate the process of elimination of Ravana and his supporters so that atleast some demons can survive and he can protect the Demon Race with the help of Sri Rama.

That was the turning point in Ramayana.  

Sri Rama was undoubtedly the greatest warrior and all Vanara-s were committed to a cause, but with out Vibhishana’s advices, it would never have been that easy for the 2 brothers to eliminate Indrajit and Ravana.