I don't understand the "heartmates" thing. Seems childish. Or like trying to fit a round peg in a square hole. Anyways...

I think you do have a secure attachment to your T. I think you are actually insecure with yourself. Those insecurities you project onto your T when something triggers you.

I can finally say I have a secure attachment to my T. Of course, I have insecurities due to my past, and I too get triggered and project it onto my T. She knows this. She just reassures me, has me recount our times together, and reminds me it was all in the past. Then I go back to feeling secure with her again.

I guess you need to separate the past from the present. Old you, new you. Triggers, reality. If you're not triggered, you trust your T, right? And triggers come from the past. So the reality is that you do trust your T.