Who is the antagonist in TSB , and what is the conflict between Cole said antagonist?

I think you need to view this in a wider context. Cole's is primarily an internal conflict. He must come to terms with his own pain before he can make any progress in his life. The Spirit bear acts as both a metaphor of Cole's demons as well as a to reduce Cole to his essence. Only then can Cole be reborn with a new understanding of his life.