Hello ArmyTrainer: Well... it seems to the Skeezyks that the significant thing here is your stepmom does not seem to share your perspective... at least not from what you wrote. You wrote that you cannot wait for the divorce to be final so you can go after what you want. Well... you can try. But if your stepmom is not interested, then there is nothing for you to go after. (Consider that it is possible she told your father about your feelings as a way of hurting him. And if that is the case, then I would conclude this says something about your stepmom's feelings for you.)
Divorce creates all sorts of emotions... anger, embarrassment, fear, & probably several others I'm not thinking of at the moment. This is likely a very vulnerable time in your stepmom's life, especially considering that she is in her late 40's. People tend to become less resilient as they age. So, with all of that said, my personal perspective is, if you do really care for your stepmom, you will give her the space she is going to need in order to heal from this traumatic experience.
And, during that period of time, it might be wise for you to seek some therapy to help you sort through your own feelings. Far be it from me to suggest there is anything inherently wrong with a 23 year old being in love with someone who is in her late 40's. But, speaking as an even older person, I will tell you there is a world of difference between those two ages. Even if in the end the two of you would end up together, you will both face some unique challenges over the ensuing years. I wish you well...