Your friend is a Christian, you spent all of last year going to church together on Sunday and then she comes back this year and says she's "not that into it anymore" or she smokes weed, hangs out with the wrong group, whatever it is - she's not the same and she seems lost.
Your best friend comes out as gay, you grew up in a strong Christian home and somehow have been taught the misconception that being gay is a sin, so as a result, your friendship suffers and you two become distant.
You either know, have seen, or have been in similar situations. Situations where someone close to you or someone you know, does something that you disagree with morally. Something that you inherently believe to be wrong or bad. So, as a result, you become angry, upset, distant, etc. But that wrong act or sin, doesn't make up that entire person. It is merely a piece of their whole. It's either something they're battling constantly or struggling with. But they're still human, with a heart, a mind to think, create, love, and decide and they are still deserving of your love.
The minute you wrap up sin and a person together, the devil wins.
He wants you to see that sin as a person in their entirety. The devil doesn't know mercy, grace, forgiveness, or real love. You can still love the person who is gay, even if you're Christian. (shocker right??) However, that doesn't mean you have to love and support any gay action, like gay marriage for instance. Because more often than not, Christians believe and know marriage to be a holy bond between a man and woman. And that's okay. But gay marriage is potentially just a part of that gay best friend of yours, and they're still human, and still worthy of love.
Separate the sin from the person. Separate the wrong from the best friend you know and love. And in loving them, help them out of that sin, sit and listen and discuss and share. Offer forgiveness. Offer mercy. Offer grace. Love the person, not the sin.