So why was someone actively engaged in a homosexual lifestyle allowed to participate in ministry in the first place? I recognize that people can struggle with same-sex attraction and still be able to serve in ministry - as long as they are not submitting to that temptation. Anyone who is actively involved in sin should not be in ministry - whether that sin is homosexual activity, adultery, fornication (sex outside of marriage), drug abuse, alcohol abuse, theft, etc.
The issue is not that homosexuality is a worse sin than any other - it is that for most people caught up in it, it is a sin that defines their whole life and becomes a part of their very identity. And when people who are known mainly by the sin they practice are allowed in ministry, it brings disrepute to the Church of Christ.
So in answer to your question of how was he allowed to be in ministry? Well no one probably knew for sure that he was engaged in a homosexual relationship until he told everyone.