You are going to get a lot of grief here about being married and cheating on your wife, whether it's with a man or a woman. No matter how loveless your marriage is, you have no moral right to start a relationship or even just have sex with someone else.
My .02 is that people need to get off the moral soapbox here. It's not constructive, really. You know...those without sins...throwing stones...
Anyhow, might I suggest you re-think your telling your wife about this "no matter what?" These things are tricky, and there are legal implications. One such implication is that she could sue you for adultery and her lawyers could subpoena your 20 year old friend as a witness (it's happened). That would be pretty mortifying.
If you want to come out to your wife, that's another matter. But, be strategic in how much information you want to disclose--both for legal reasons as well as for her emotional and psychological welfare. But, there too, think through how much you want her to know and how it may, or may not, come back and haunt you.
I'm a firm believer that people are entitled to as much information as they can handle. If she's anything like your church acquaintances, it's not much. What a bunch of garbage...you "weren't born that way?" "You chose to be gay?" My God, are they living in the 1950's? (Don't answer that). Did they "choose" to be straight? Could they "choose" to be gay if they wanted to? Of course not. Try throwing such silly comments back at them and they'll realize the fallacy of their logic (if you care enough to).
Good luck. You're not alone, even though it may feel like it. I hope you can extricate yourself from your marriage easily and gracefully, if that's what you want to do. And, I hope you do so with as little trauma to your wife and yourself as possible.
Finally, try to tune out all the self-righteous, holier-than-thou, judgments about coming-to-terms and experimenting with sex during a marriage. Sometimes it just happens this way. No one wanted it to, but it just does. Just tell these people to grow up, you're doing the best you can, and to mind their own business.