I thought that the pope’s decisions were infallible on doctrinal issues. Therefore, by reversing the church’s position regarding priests marriage, he is saying that the previous popes were all wrong when they required priests to be single.
Nope; it’s not a doctrine or dogma that can’t change, it’s a discipline (an internal, transitory rule) which has changed back and forth over the centuries according to the needs of the time. If the Pope saw fit to get rid of it he could.
Matters of custom or discipline don't fall into that category. The argument that priests must be male is regarded as a matter of doctrine. That RC priests may not marry is a matter of discipline, was not always true, and may be changed.
Of the 22 Churches (Melkite, Maronite, Ruthenian, Chaldean, Greek Byzantine, etc) which make up the Catholic Church, only one of them (the Latin one) chooses not to ordain married men, and even this is not true in every case. For instance, married Anglican priests who convert to Catholicism and are accepted as Catholic (Latin) priests, can keep their wives! If they were widowed, though, they may not remarry.
Not correct...unmarried clergy is merely a rule, the Pope can, indeed, revoke the rule....I don't think that he will....no good reason whatsoever.