Heather,
It sounds to me like you are a transvestite or cross-dresser. This is the more masculine end of the transgender spectrum. If I offered you a magic potion that would turn you into a beautiful woman, 5'9", with a pretty voice, nice figure, be a perfect size 7, and have an otherwise nice body, face, voice, and personality, but once you drank it, you could never change back - would you drink it?
You could still watch NASCAR, football, and enjoy sex with women or men. You would not be able to fight. You wouldn't have upper body strength. You would have to take care of your hair, legs, and other aspects of being a woman. You could wear pants and sweatshirts when you wanted to, but you'd always fill it out like a woman. Would you drink the potion?
If the answer to that question was an unqualified yes, then you might be a transsexual in spirit, but a cross-dresser in practice. This is probably the hardest situation of all, because our bodies have betrayed us so badly. In my own case, when I considered transition back in 1988, I weighed over 275 lbs, had a beard and facial hair. When I began to explore the possibility of transition, I lost over 120 lbs, I also did exercises to form by body in a more feminine way. Talking was still a bit of a problem, but I could at least pitch it close to middle-C, which was "good enough". The key here was that transition was a strong motivator and was something I really wanted to do.
When I was forced to stop transition (or risk losing access to my children), I gained weight, growing to 320 lbs, grew a beard a few times, and eventually had a heart attack and a stroke. When I recovered, I started looking at transition as a way to get my health back. The surprising thing is that it WORKED. Again, it was a strong motivator and I fully recovered from the stroke, lost 85 lbs (235 lbs), and WAXED off my beard. I also started laser (Tria), and started seeing a gender counselor. I even started hormones.
When my wife tried to stop the transition, I became suicidal, started gaining weight (about 40 lbs), and work suffered. When we talked it over, addressed her concerns, and looked at how we could address them, I went back to gender counseling, got back on hormones, and have lost 20 lbs.
If the thought of spending the rest of your life trapped in your male body makes you think about drinking a quart of Antifreeze with a quart of Gatorade, then you're probably transsexual. If you are more than happy with your male body, but just like dressing up once in a while, then you are probably a cross-dresser. It sounds to me like you might even be gender-queer, wanting to be able to wear certain aspects of female presentation - clothes, hair, nails, & jewelry, but without having to try to present as a woman.
These are all different degrees of being transgender. There is nothing wrong or "better" or "worse" about any of them. Many transsexuals have tried to settle for being cross-dressers and have lived that way for years, but they have known they were just "settling". Others, have been cross-dressers and have dipped their toe into the water of transsexual and transition by dressing "Full Time" - on evenings and week-ends, and realized that they did NOT want to transition.
The most important thing for you (or any other readers), is to see where you are NOW, what you are comfortable with, and where you really want to go from here.
I'm a bit concerned about your weight. This may be the result of self-destructive behavior, and you may want to look at what's at the root of that. Your risk of heart attack and/or stroke is very high, and if your blood-work is also bad, you may also have other factors such as type 2 diabetes or thyroid issues. Some of us turn to drugs, booze, or food to "commit suicide on the installment plan". Take a good look at that. Many transsexuals, trapped in an excessively male body, will begin to see reincarnation as their only hope.
As for why you feel you need to keep it secret, that's easy. Even if you weren't persecuted as a "Sissy" in elementary school, you saw what happened to those who were labeled "Sissy". You also saw what happened to those who were labeled "Queer" or "Fairy" in middle school and early high school. Often, by later in high school, there were boys who were openly gay and "out" and were not getting prosecuted, but by then you realized that many of these boys were NOT effeminate, and were in fact, strong, muscular, and athletic. For some, the intimidation can span generations. The messages can come from parents, aunts, uncles, adults at church, and other authority figures.
Even though you may trust your wife to a certain point, there is always the fear that she might reject you. Many of us have lost wives, children, parents, jobs, and friends, because we told the wrong person about our cross-dressing. Sometimes we even get a sense of "boundaries", like "I can accept that you want to wear silky panties, but thank goodness you don't want to be a girl, because I couldn't handle that. Often, we try to spoon-feed our spouses and loved ones what we think they can handle. It can be a real struggle and genuine conflict because we feel that we have to choose between being who we really are and our wives, children, parents, friends, and jobs. As one who has lost EVERYTHING at least once, it's a struggle for me to be honest with my current wife. There were even points where I finally broke down and said "If you can't be Debbie's Wife, you might be Rex's Widow". Thank God I got help before I took the "final action", but I should never have let it reach that point in the first place.
Much of this can also be part of your culture. If you live in a city that is more tolerant, like San Francisco, New York, or South Beach Florida, there is lots of support for diversity of sexual preference and sexual identity. On the other hand, if you live in a small red-neck town in West VA or Texas, even the slightest deviations could become life-threatening situations. Sometimes, moving to a "college town" can give you a bit more freedom, but it's still pretty intimidating if you're living in the "Bible Belt" and getting lots of negative messages.
You might want to let your wife know about this website too. She probably has questions of her own, concerns and fears of her own. You may need to talk to others in these sites before talking to each other, but ultimately, you can explore your concerns together, work them out, and make sure that you are able to grow together.