There is no easy answer to your questions. Everyone is different.
I can give you a quick summary of myself, if anecdotal data is what you'd like:
Closet cross dresser from about the onset of puberty until about 2 years ago. Mostly borrowed girl friends clothes when they weren't around.
Lots of denial and purging throughout my life, but I was never caught dressing or told anyone.
Divorced about 4 years, with a daughter who spends half of her time with me.
Living (partly) by myself just a few years ago, I started buying my own clothes, after the divorce.
I turned 40 and something "clicked" in my brain. I had pretty clothes but no where to wear them...
Got online to look for "cross-dresser" events and didn't take long before I found one 2 hours away.
I went to my first GNO and no one would believe me that it was my first time "out"... ever.
It was one of the greatest experiences of my life and that night Lexi was born.
It wasn't long after that I realized how much I dislike being a guy... pretending for so long... finally realizing that I am transgender.
Started going to more events and making lots of TG friends.
Last winter came and it was a serious personal struggle. Realizing that I'm transgender and that I could never go back to a life of pretending.
By the end of Spring, Lexi won the argument and I started transitioning with Hormone Replacement Therapy (HRT) in the summer.
Here I am about 7 months later and my only regret is that I didn't figure it out sooner. Wish transition was an option for me when I was younger.
As for Sexual Orientation:
I spent my first 40 years as a straight guy... all my experiences were with women. But I've always had fantasies about not limiting myself to such a narrow end of the sexual spectrum.
I consider myself Pansexual. I find that I'm attracted to the person, not what happens to be between their legs.
After coming out as trans less than 2 years ago, I finally had sexual experiences with men and trans-women alike.
I don't mind telling people about my experiences because now I really know what I like and dislike. How do you know you don't like green eggs and ham if you've never tried it?
At this moment, I'm still heavily attracted to women and cis-women are at the top of the list. Guys and their penis controlled minds are such a turnoff for me. But I still have the occasional fleeting fantasy when I meet a certain guy that I feel myself attracted to. I don't have control of it, it just hits me.
I have a cis-girlfriend that I met after coming out and she's only ever known me as Lexi. She has the same concerns as you... Asks me, "What happens when you want a man?"
I just tell her... "I'm not interested in guys. I've been with guys. Just not what I'm looking for right now"
I'd guess you're husband has some attraction to men. He might not want to admit it, or might be in complete denial to himself. It's quite natural. I don't believe that anyone is 100% straight, and there is lots of scientific evidence to back that up.
The sexual arousal associated with "dressing" usually dissipates after it becomes more routine. Oh, and taking female hormones will kill that quick too!
Lucky for me, I didn't have a relationship / marriage to worry about when I finally came out. Hats off to the couples that find a way to make it work.
The long and short of it: Everyone is different, but it's a journey and everyone moves at their own pace.