Hey there First off it is to be expected that one friend might change their perspective on you if you are homosexual. That doesn't make it fair, nor does it make it right but it is the harsh reality of the situation. Someone who is really close to you probably wouldn't have been surprised at you coming out. This indicates that the person probably wasn't as good of a friend as you had previously assumed. What you will learn from this situation is who your true friends are. Whomever stands beside you and isn't ashamed to be friends with the "gay guy" is a great friend and someone that you should cherish and keep close to you.
About your other friends; do you know how they are handling it? Is everyone else treating you different as well? Even if they treat you different in a good way; you should remind them that just because you are gay doesn't make you any different. Often people mold into the stereotypes automatically. For instance; my friend Caleb came out Freshman year. Immediately I saw girls trying to take him on "shopping dates" and stuff like that, but it was dumb because he always hated shopping before. Just because you are gay doesn't mean taht you mold into the basic cliche. (Not that some don't.) People who treat you different really didn't know you before.
It takes a lot for someone who is homosexual to show the world who they are so I really want to commend you on being honest with yourself and others. Not a lot of people can handle it.
To answer your questions:
What should I say?
if people talk to you about it just explain to them that you couldn't handle lying to them anymore. Tell them that you really care about them so you can't bear to not have them know the real you. Hearing this will probably make them feel guilty for thinking any different of you. You will find new friends and keep some true old ones because of this. Look at this as a great thing because it really will help you weed out the people who don't care about you.
What should I do? Whatever you were doing before is what you should continue to do. Get back into your regular routine. If people see that you really are the same person they will feel stupid for thinking that just because you announced you are homosexual that you have changed. Just be yourself and have faith in knowing that you are completely honest about 100 % of yourself now. It takes a lot of courage to stand up and say "I'm gay." Obviously you accidently told the wrong person, but that's okay it happens. Sometimes you don't know exactly who you can trust. All you can do now is embrace the truth and move on.
I would like to ask if your parents happened to find out. Did the news from the grapevine somehow get back to them? If so, how are they handling it? If it hasn't got back to them yet, I would like to encourage you to be the first one to tell them. I'm sure that they would take it a lot better hearing things from you then being the last one to hear. It's never fun to be the last to know. It's going to be hard telling your parents as it is. At least they can respect that you were the first to tell them.
If you have any further questions or need any more advice, respond either on here or via PM.
Thank you!
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Antidisestablishmentarianism.