Under which Canon law?
The believers in Jesus Christ who do not submit to the tyranny of Rome (the Vatican, whatever...) would be completely free to simply tell the man, his support of homosexuality is unbiblically sinful and we would no longer fellowship with him. And that would occur under I Corinthians 5:11. You guys stay right there enslaved to canon law, we’ll continue to use the Bible.
Canon 751: Heresy is the obstinate denial or obstinate doubt after the reception of baptism of some truth which is to be believed by divine and Catholic faith; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Supreme Pontiff or of communion with the members of the Church subject to him. Canon 1364 §1: an apostate from the faith, a heretic, or a schismatic incurs a latae sententiae excommunication. The phrase latae sententiae means a judgment or sentence which is 'wide' (latae) or widely applied; it refers to a type of excommunication which is automatic. Such a sentence of excommunication is incurred by the very commission of the offense, (CCC 2272) and does not require the future particular judgment of a case by competent authority. Apostasy, heresy, and schism are all offences which incur a sentence of excommunication automatically. Heresy is the obstinate denial of any truth of the Catholic faith, on a matter of faith or morals, which has been definitively taught by the Magisterium. http://www.catholicplanet.com/articles/article78.htm