Yea, it sounds like you've got a fairly common fear: you're picking for forever. That's totally not the case. The average US worker apparently has between 3-5 careers is their life, time, so I'm sure you can have two. Just know when it's time to transition and how to do it. Steve transitioned from video game entrpreneur to personal dev person, etc.
The decision is not permanent and neither is it either/or. Any good school you go to will likely have a theater club or something where you can do this sort of thing. And if you get really good, you can often audition for plays put on by the school itself. It may take more effort to work on both, but if, as you say, you like 'em both and find them rewarding then it'll be worht it. Many artists work across mediums, many do. MIA comes to mind as a popular example off the top of my head. I'm sure you coudl think of more of them if you tried.
Chill out, you can always choose again. There may be consequences, but you can learn to handle them pretty well. Good luck!
I can tell you this, though: follow your heart now and pick either one, or stay stuck and be garunteed a life of mediocrity and safety.