I'm a bit upset at my Christian friends for not wanting to come to my birthday because of the location.
Where are you having the party?
I invited them to my gay friend's house party.
I assume they have an issue with your friend being gay, right? If they want to be close-minded and not attend your party, that's just how it'll be.
People say that God hates fags. I don't think he is so petty to deny me my happy day.
I wouldn't worry about how they feel about your friend. Just enjoy your birthday and let them be.