Good question. I don't know.
I'm struggling with that. We must minister to the sinners, but cannot condone their sins. How can we turn away sinners who come to us? I've committed sins since joining my church. Should I be forced out? I'm pretty sure some of the people in church with me have done the same. And it should come as no surprise to anyone that this happens.
Where I would draw the line is if this person stated their open homosexuality, expressed an intent to continue as a practicing homosexual, and denied that it was a sin. Then I would deny membership. I've seen many new members admitted and I have to confess I kind of zone out when the pastor goes through the oath of membership. But I believe one of the lines is "Do you truly repent of your sins..." or something like that. An expressed intent to continue with homosexual practices is a violation of the oath even as it's being given.
I would still encourage attendance for this person. Can't give up on saving someone.
Pending any evidence to the contrary, this is most likely how the minister discovered the problem in the first place.