Translation:I have no interest in him.
他 is treated as the object, whereas 我 is treated as the subject. In the given sentence, 对 is treated as the "relationship" verb (which can be thought as "to treat" or "towards") between a subject and an object.
If the given sentence is
then the literal built blocks are
I "treat" him without interest.
I do not have interest in him.
More info is here.