I had the same feeling in my 20s.
I'm now in my 30s, and the biggest regret I have in life is that I lost a relationship because I needed to "accomplish something before I ran out of time". Even though I had no absolutely idea what that "something" actually was.
It's a horrible, depressing realization.
To anyone reading this - please, please don't jeopardise a relationship because you feel unsettled or anxious about the future. You can backtrack from most mistakes in life, but a broken relationship is not one of them.