It is optional to include or exclude a parallel structure in a comparison
He is closer to than my brother is close to me
may be shortened to
He is closer to me than my brother is
which may in turn be shortened to
He is closer to me than my brother.
Notice that, in the wordiest version, the comparative clause is identical except for the degree of the adjective: "close" is not in comparative degree. But "closer than" implies "close" in the comparison.
But a structure that is not parallel cannot not be omitted.
He is closer to me than my brother used to be close to me
can be shortened only to
He is closer to me than my brother used to be.
Your final version is wrong because it omits the verb from what is a clause.