I know I am cheating on her but the alternative is coming out and telling people and that is not an option.
First up - I'm really sorry man. I'm sorry that you're in this situation, I'm sorry that you're dealing with this...you have my sympathies. You're still young and still figuring things out. The number one biggest thing, though, is not to tell yourself you're "stuck". You
always have choices. You may not
like the options you have on the table, but if you think about things from different perspectives, I think you'll get some clarity.
As others have pointed out, if things were reversed and your wife decided she wanted to try having secret sex with women and not tell you about it...you'd be really hurt. And there's the issue of safe sex...even when you're trying to be safe, it's possible to catch something and then pass that onto your spouse. I'm pretty sure you don't want to do that to your wife...but since you said you've already have numerous one-night stands, I think you're in a bit of denial.
I mean, you're mentally hoping that you'll get a boyfriend while in Afghanistan - process that for a second. You're actively, intentionally saying you want to have an intimate, on-going relationship with a man. And you're asking us if we think that will have an affect on your marriage. I think you're smart enough to know the answer is yes.
It's not about whether you love your wife or not - it's about whether you want to be free to have sex and relationships with other people, or whether you
only want her. It doesn't sound like you only want her, man. It sounds like you want to be single. Because you're living the single life already, in secret. If you let her go on thinking she's married to someone, you're fooling her and hurting her, and that's not right.
I get that there is this "story" out there for bi men - that they can live with a wife for 40+ years, but have their secret gay adventures on the side, and everything works out okay. But the question is whether or not you respect yourself and your wife enough to lie and deceive both of you like that.
At this point, you've already cheated, and told yourself it was okay, so long as you didn't tell your wife. You're not respecting her at all, and so...I think you need to tell her. I think you've already decided you're going to cheat in Afghanistan, and she shouldn't be stuck here, thinking you're Mister Terrific and probably hating herself for feeling sexually unfulfilled in your absence. Be a
real man, be honest with her, and tell her now. You've already done damage to her that you're not facing up to yet.
The only way you're ever going to feel good about yourself is if you treat this woman - the one who pledged her life to you - with enough respect to fess up that you're bi and have cheated, and then let her think about it and process it.
Remember how you said "Telling her is not an option"? Well, what you're really saying there is "I want to have my wife and my "marriage" and my gay affairs and lie about it and never get caught and let everyone think I'm this honest, devoted hero of a husband." That's not the truth. I'm not saying that to be a jerk, but it's really not the truth.
If you want to be an honest person, if you want to start making up for all the lies, if you want to a real hero...tell her now. Yes, she will hate you and she will be upset and confused...but most importantly, you'll be freeing yourself up from a life of running around, being afraid of getting caught as someone in the closet.
Speak to a therapist if you can before you go. I think you're really in denial about the choices you're making and need to have someone to talk to who isn't in your life and won't judge you. In short: you need some help, man.
And again - I'm not judging you. I don't know you, and you're going to make up your own mind about what's right and what's wrong and what's acceptable to you. I just think you'll be a lot happier when you own the fact that you're bi, and when you can have sex and know that it's totally okay.