Hi! I'm here to try to answer some of your questions and hopefully make the experience you're about to have a little easier.
There's a standard coming-out narrative that is available to most gay men. It takes two main forms: "I never liked women," and/or, "I was dating [or engaged or married to] women because I didn't realize I was gay [or I was hiding the fact that I'm gay, or I was trying to change]." For us bi guys, those two options don't work quite as well, because we have been and are genuinely attracted to women, and we are also genuinely attracted to men (and quite a lot of us are genuinely attracted to people who transcend gender altogether). This seems to complicate things, but it really doesn't, at least not for you. You know who you are.
Coming out is not easy to do, but it's the lifting of a giant weight off your shoulders. When you're out, you get to live without fear of blowing your cover. That alone is a huge benefit for you, because not being able to stand up for yourself out of fear is emasculating -- and one of the ignorant and hateful things that people say about queer men is that they are not "real" men. I know: My ex-wife used to throw that one in my face, along with my mother, my peers and pretty much all of society. It's OK. There is no actual "man law." No one can take away your "man card," because there is no such thing. That's just crap that men who are insecure about their own masculinity make up because someone told them they weren't "real" men, so they try to do it to everyone else. The most important thing is to be yourself. If feeling masculine is important to you, know that being bi doesn't change the man you are.
Coming out as bi is going to confuse a lot of people, and because of this, a lot of people are going to say some really, really stupid things. They may try to tell you that you're confused. If you are married to a woman, they may assume that you're going to get divorced, or that you don't really love your wife and are just using her as a maid and a babysitter, and that you're just out having fun while she's crying alone and neglected at home. If you are divorced, they may assume that your sexuality is the reason for the divorce. And if you're single, they may assume that you have no real interest in women: "Ah, that's why he's never settled down!" But you and I know that that's not the truth. But the people making these assumptions are people who only understand sexuality on their own terms and aren't making the effort to see how things really are for you. The good news is that that's their problem, not yours.
All you are obligated to do is be who you are. You don't have to explain everything to them unless you want to; all you have to say is, "I'm bi." If they want to argue with you that everybody is bi so nobody is bi, or that you're really just gay and pretending to like women, or that because you're married or involved with a woman, you should just keep it to yourself, you can smile and walk away, you can point them to the Internet resources listed below, or you can explain to them the simple truth: "I am who I am, I like whom I like, and I'd appreciate it if you'd accept me on my own terms. If you can't handle this like an adult, then I have better things to do than argue."
A lot of men who are reasonably high-profile have come out as bi or profess to reject labels altogether, saying things like, "Well, I just don't use any label for my sexual orientation. I'm just not straight." However, "not straight" is a label, and for most people outside bisexual circles, it is a synonym for "gay," for being attracted only to guys. Even the men who clearly say they are bi frequently get labeled as "gay," and it's going to happen to you. "Gay" is not a dirty word. There's nothing wrong with being gay. But for you and I, it's just not accurate, because we're not attracted only to men. It's not that we're "afraid to be gay"; it's that the raft of assumptions that come with the word can cause problems.
A lot of people are going to try to be supportive by saying, "Gay or straight, you're still the same guy." These people mean well, and they are genuinely trying to be your allies. They may not get it right away, but you'll have plenty of time to explain to them (or have someone else explain to them) what being bi really means. Don't lose heart.
One of the most important things for you to do when you come out is to find a supportive community, either in the flesh or on the Internet. If you are lucky enough to live near what people tend to call a "gay city," there are resources for you: NYABN for New York, BRC for Boston, BOP for the Twin Cities, BABN for the San Francisco Bay Area, amBI and LABTF for Los Angeles, and others for D.C., Houston, Austin, Chicago, Denver and Salt Lake City, for example. There are other cities and places with bi-specific resources, so this is by no means an exhaustive list, and some of these cities have multiple resources. And if your search for community is limited to the Internet because of your geography, those sites have lots of links, and there are thriving bi communities on social media platforms as well as places like BiNET USA and Bi.org, which is a portal with a lot of links for UK organizations.
Reach out and join the bisexual community. Knowing them -- knowing us -- will help you, and by joining the community you also make it larger, and thus you make it easier for the next bi guy to come out and be himself on his own terms. Some queer communities are welcoming to bisexuals, and some are not. If you find yourself being rejected by your local gay community, don't go back in the closet. Again, it's their problem, not something wrong with you.
If you are married and the reason you're coming out is that you've finally figured out who you are, and you're currently doing that very first coming out, the coming out to yourself, your wife is the first person you should consider talking to after you've accepted your bisexuality yourself. There's a pretty good chance that she's known this for a long time (or, if you're like a lot of us, she has been the only person you've always been out to). If it will be a surprise for her, make sure that you come out to her simply and clearly. It shouldn't be a big production, but it also shouldn't be an offhand "oh, yeah, I'm bi" while you are heading out the door somewhere. Be prepared for it to take some time and to require an open and honest conversation. If you are not planning to have sex outside your relationship, let her know that. If you feel that you do need to reach out to other men in a physical way, she should know that, too, and how you handle that will have to be something you decide together.
In either case, you will have to do some renegotiation of your relationship boundaries. They may end up in exactly the same place they were; my partner and I have renegotiated several times, and the boundaries have not moved. By renegotiating, even when they don't change, we've been able to be sure that we're both seeing them in the same place.
If you are going into a relationship with anyone, gay or straight, be sure to let them know. Honesty is never a bad foundation for a relationship.
If you have a therapist, talk to them about it -- but if they immediately tell you that you're on the fence, that you're really gay, or if they assume that you want a divorce for that reason, then you should ask them for a referral to someone who understands bisexuality. Remember that as a client, it is your fundamental right to find a therapist who will understand you on your own terms.
If, after you've identified as bi for a while, it turns out that your attraction to women isn't a real thing, that in retrospect it was an act or something forced on you, that's OK, too. You have every right to be fluid and to change how you label. However, bi guys ask you not to assume that what was true for you in this case is true for everyone. A lot of gay men have done damage to their bi brethren by telling them that everybody is really gay or really straight, that they're just confused or lying.
OK, bi guy, I hope this helps. I and lots of others are here for you. Be who you are, and you'll be fabulous.
A different and longer version of this blog post previously appeared at Eponymous Fliponymous.