What do you think about me being a guy in a committed hetero relationship who secretly would love to be someone's wife.
Thats an interesting thought to have. Does it go deeper than that?
I fantasize about running away to a beach with a lover.
If you are confused about your sexual preferences, you should be honest with yourself and your spouse. Therapy could help you figure out your feelings. But running away from your problems won't be a good solution.
I don't need to, what I want is simply impossible. I just want to be more free to express my femininity.
If you truly would like to be more feminine, then you should speak with your wife and let her know your feelings. She may be very accepting of you wanting to do more typically-female things with her.