Dear Dianna: Hey girlfriend, good to see you back.
I'm no guy, but it seems the fact you "couldn't choose if you had to" between the two ladies in your life right now probably indicates serious and exclusive to either one isn't right for you, at this time anyway.
In my experience, an inner sense of "knowing" happens at some point, and then serious and exclusive makes sense. Until then....you're not ready.
You just got single again, so perhaps you need more time to just date and have fun. No shame in that.
Guys??