It sounds like you are having flashbacks that encourage you to feel fear. If a person struggles with PTSD, for some reason old situations that caused emotional confusion can come forward. The best way to deal with that is recognize that "did" happen, that at the time you did not handle it in a way that the other person felt ok with and for some reason, now that you have gained so much more life experience and maturity, you wish you could have a redo.

It sounds like you had a friend that wanted to have more of a relationship with you then just a friend. You have no control over that, what that means is the other person needs to get over the disappointment and mature more. It's not your responsibility to "mother" that other individual or feel guilty because that other individual was in some way disappointed and probably drew a mental map of you that could never exist.

You seem to be stuck in this loop of fear and guilt, acknowledge that and encourage yourself that it's ok for you to move on even when things don't go so well when interacting with others. I think that with PTSD, often a loop can develop around "guilt", it's important to recognize that, acknowledge how you feel and give yourself permission to accept that that one relationship just did not go well and it's really not your fault and you should not be feeling so much guilt. I know that can be a challenge, it was so good that you wrote this challenge out and articualted it so you can work on slowly resolving it. PTSD does present these challenges, and they do come on as a "magnified" challenge. You can get so you understand this and reduce these challenges gradually, PATIENCE is the key.