Sorry to hear your story, acquilon. I can't understand, in this day and age, why anyone (other than religious bigots) think that it's an issue.
A few years ago a friend of mine, at a house party weekend, asked if he could fetch over a friend the following day. He then explained that it was a 'he', not a 'she'. He was clearly very stressed (and, in fact, had been stressing about this double life for nearly four years previously). He didn't get the reaction that he was expecting. We all said it was not a problem, no-one was in the slightest bit bothered. The flood of relief from him was such a joy to see. We've met his partner now on many, many occasions and he's just "one of the gang".
"Friends" that can be so intolerant of other people's lives and preferences are simply not worth having.
Give your friend a wide berth and tell him that when/if he comes around to the idea that you'll still be there and happy to continue the friendship. If he doesn't then it's his loss and when he gets older he'll be the one regretting letting a good friendship go.
I appreciate that you're probably mourning the loss of a long-time friend but it's his problem to sort out, not yours. Seek the support of other friends who are less subjective. Personally, I hope that he comes to his senses and ditches the nineteenth century Puritan attitude. Society develops, attitudes change, tolerance spreads (or should) in civilised society.