Hi there, I'm so sorry you feel like this.. Limited to what you said.. it might be that you are afraid that the worst is yet to come.. Your previous relationship wasn't good and with toxic relationships, they don't happen from day one, they build until they go bad.. Maybe you are afraid history will repeat itself..
But it can also be that he did something or said something that made you uncomfortable and that brought in this feeling of wanting to get away.
Someone you really loved and trusted broke your heart. I can totally understand why you'd feel this way..
But in the long run, it won't help if you want to get away from everything. If you feel safe with him, you should discuss this feeling with him; talk to him about you past relationship (if you are comfortable) and what makes you want to run away..
You should also consider talking to a therapist because they will help you dig deeper and help you identify what is causing all this fear and hesitation and help you overcome it.
I really hope this helped.