My boss seems very opposed to me/biased against me/ against me / - lately, as in he's writing off my ideas and initiatives unfairly and is very critical towards me unreasonable.
If you feel he is rejecting your ideas simply because they come from you and not because of the ideas, then you would be correct to say, "He is biased against me."
More or less, yes. When he is biased he leans in a certain direction. When he is prejudiced, he tends to not accept you or your position or he is generally negative towards you...