Telling another person you're gay is normally a big deal for someone. If the person they're telling is Christian, it is likely to be an even bigger deal. Many people assume Christians are anti-gay, and it is not a huge leap from that to think Christians must be against gay people themselves.
So the first thing you should do is thank them for being so open, and entrusting something so personal to you. It is a privilege to be told such things.
It is also important to assure them that their fears of being rejected by you are unfounded.
Knowing they are gay should not mean you stop liking them or being their friend. In the interests of full disclosure - and especially if they ask you what you think about it - you might flag up that Christians have a different take on matters of sexuality than the culture does as a whole, and that you'd be happy to chat about that some time. But this may not be the moment.
Listen to them. It is good to ask people a bit about their experiences of homosexuality. How did they come to this realisation about themselves? What kind of reactions have they had from other people - their friends and family? Has it been a hard time for them? Are they doing OK? We need to find out about their story and its ups and downs.
Understanding more of their background and experience will help us know how to be a good friend to them.
For more, see Sam Allberry's book, Is God anti-gay?
- Marriage and sexuality