How do I stop a 'planned future' from blindly determining my life's path?

For most of my teens I (21) had a broad but distinct vision for what I wanted my 20s to look like. It was everything I liked, I was looking forward to it, and was planning around it. Unfortunately it now seems that a central tenet of that vision will not be possible and I'm gonna have to rethink my 20s to suddenly look radically different (not sure how yet) to what I had come to anticipate. What's more, some of the things outside of my influence that I was sorta expecting to have happened by now (first kiss etc) haven't and I've found myself waiting around for them before I feel prepared to move on (they were part of the vision).

Unfortunately, since I had come to identify myself with and live in expectation of this path for my 20s, even when the central thing became impossible I tried to salvage the rest and make the side things still happen – which, as I have found, takes much more effort without that central thing tying them together. Since I've been planning around it for so long, I've sort of forgotten what alternatives there are so I don't even know what else could be right for me (or how to find that out).

I think what makes it so hard to abandon the future I was expecting is that it gave me a sense of identity. This might also be because I didn't like the life my parents had arranged for me during my teens. I'm afraid that if I try to go with the flow, embrace my actual (unhappy) reality and don't try to correct my course to at least partially replicate the future that was supposed to happen, I would eventually become a different person, which discomforts me. It's also the reason I'm afraid to try new things that could distract me from the (albeit now impossible) trajectory that I have come to identify with.

I guess this really leads me to ask what the bigger mistake that I'm making is. Why do I constantly need this future path/plan of experiences to guide me and give my life a feeling of meaning? How do I learn to let go and embrace whatever I'm served by life and live in the present without caring about where the path leads? I liked the feeling of certainty that having a (retrospective, almost?) vision of the future gave me but it made me a control freak.

TL;DR: I blindly made my life decisions based on a future path that is now long obsolete, but gave me a sense of identity and my life/struggle meaning. How can I let go of it so that I can embrace my actual situation and retain my identity whilst on a path that may end up looking completely different and unfamiliar?