The thing is that sometimes in therapy it's not so much that mistrusting a therapist is an issue but rather mistrusting your own reactions.

I have a feeling that you know that your therapist has good intentions and is genuinely trying to help you. It sounds like your reasonable part is in conflict with your emotional reactions that get created automatically regardless of how well the therapist is doing his job.

These reactions of mistrust are usually a "preparation" for "what if" scenario. It's as if some part of you was saying "yeah, sure, he is doing great for NOW, but who knows what happens in the future? who can guarantee that this will continue forever? you'd better be ready for anything to happen...just in case.." This is an absolutely normal protective mechanism of someone with your history of cptsd. Instead of seeing this as an "issue", I'd accept it as a normal part of your process.

Trusting others essentially boils down to trusting yourself in the sense that you trust that no matter what the other person might do, you'll be okay, you'll have the strengths to deal with it. When you are confident in your ability to handle whatever life sends your way, be it disappointments, betrayals and other relational challenges, you are no longer concerned about trusting the other person. To trust or not to trust is no longer an issue. You don't care about it much because you trust yourself. And, since you don't care about much..you can afford to trust them..:-)

Also, trust is not an absolute concept. You can't trust anyone about everything simply because people have their limitations. For instance, when I work with someone, I can trust their good intentions but not always their capacity to do what needs to be done because they may lack competence in that area. Or I can trust that someone will do something for me because it will benefit them as well, not because they have a big heart necessarily.

In that sense, I would not trust your therapist's promise that he will never abandon you not because I don't trust his sincerity ( I do believe that he wants to make good on that promise), but because he doesn't know what might happen in the future. What if, God forbid, he gets run over by a car tomorrow and ends up dead? For you this may feel like an abandonment even though it is not an actual abandonment. Or his family situation might change and he might need to relocate? Or, in a less extreme and more casual case, he, at some point, may not feel competent enough to continue working with you and refers you out? That'd feel like abandonment as well.

Again, I do believe that he is planning on continuing to work with you until you don't need him anymore and isn't planning on going anywhere, but no one knows what the future holds for them. I think, it wasn't smart of him to make such a promise to you.

This is not the first time I hear people say that their therapists promised that they'll never abandon them, and it's beyond my understanding how can anyone promise that to anyone else. And, sadly, there are cases when such promises have not been kept, again, not because the therapists didn't want to keep them, but because the circumstances changed and they had to abandon their clients.

So, don't beat up yourself for not being able to trust your therapist and not being able to change that. It's totally normal in your case. Just try to trust the reality that this process is important for you at this time and so you will trust that it will take you where you need to be next.