Is trying to manifest my ex back will block me from getting someone better?
I would say yes. You would be focusing on getting back with your ex, when your energies could be directed towards someone else. Or directed towards feeling better about yourself, so that you attract someone in line with that vibration. They are exes for a reason and that is that you no longer suit each other. A new person will be better suited to the person you are now, so aim for attracting them instead.
Yes, you are limiting yourself to just that one option when there could be loads more and better waiting for you.
If you cannot take anyone but your ex for an answer then you may be blind to the other options around you. That doesn't mean that those options don't exist, though. Focusing on the qualities you like about your ex or even your ex wont stop other people from coming into your life.
this coach can really help:
“Now imagine what a relationship with “The One” might feel like. Don’t try to picture what your partner looks like or who they are in the world. Instead, try to imagine what it might feel like to actually have this relationship. Imagine this person sitting in front of you, breathing in unison with your breath, his heart beating in unison with your heartbeat. Imagine laughing freely, crying freely, and telling him a secret about yourself, knowing that you will not be judged but only valued and loved. Imagine what it is like to know that you are this safe, this appreciated, and this cherished. This is what you are looking for. This is what you are opening yourself to.” ― Katherine Woodward Thomas,